Clamp Tonnage

By Jake Tuczapski - PDI’s Process Engineer

One concern when quoting a job is what press should be used.

This is dependent on: clamp requirements, shot size, recovery rate, press speed, available pressures, injection speeds, etc.

This Tech Tip will focus on the calculation of clamp tonnage.

First, we need to know the projected area of the entire shot. The projected area of the part is defined as the area we would see in the plan view of the mold. Either the A side or B side, whichever is greater, should be used and would include the runner in a two-plate mold. If we have a three-plate, or insulated runner, we need to consider which area is larger, the parts or runner system, and calculate from that part or system.

There are hundreds of issues involved in plastic processing. However, in this guide I am only addressing plastic flow rate during first stage.

For the following example, we will deal only with the cavity.

If we have 4 square inches of projected area and the general specification calls for 2 to 5 tons/in2, the resulting clamp requirement would be 8 to 20 tons force to hold the mold closed. Using this calculation the mold is constructed and put in a 25-ton machine for first run sampling. To your surprise the mold flashes.

Now the question arises as to why the flash occurred when a machine capable of tonnage higher than what was originally indicated was used. Simply put, the wall thickness of the part was neglected in the calculations. In the past the projected area was the only thing that people were concerned with as the part thickness was generally in the 0.100" ± 0.025" range. But, now-a-days parts as thin as 0.006" with flow-to-thickness ratios of over 200:1 are becoming increasingly common in today's molding environment. As wall thicknesses are reduced and flow lengths are increased, the resulting cavity pressures are much higher than what was previously seen in thicker walled parts. Consideration of these variables must be made when considering clamp force requirements.

The terminology of what is thick wall or thin wall can be arbitrary. Some articles and books list them as follows:

less than 100:1=thick wall

more than 100:1=thin wall

more than 200:1=thin wall with special needs

To calculate the flow-to-thickness ratio, divide the length of flow in the part by the nominal wall thickness of the part. If the flow to thickness ratio is less than100:1, the standard clamp tonnage range can be used. At 100:1, the use of upper limit values of clamp requirements is suggested. If ratios of less than 200:1 are present, the clamp tonnage to be used may exceed the standard rating by 1/2 to 2 times the normal amount. Additionally, you must consider the supports, steel selection and other mold construction methods used. ----------------------------------------------

Plastic Design International was started in 1977 in the short-run prototype R&D business. PDI is now one of the most effective Plastic Injection Molding production companies on the East Coast and an expert Mold Making manufacturer. Please contact us with any questions at 860-632-2001.

Design Considerations for the Process

from Wikipedia

It is important when designing products for injection molding that you consider how they will be formed in the machine, how they will be taken out of the machine, and the structure of the final product. Some important guidelines are:

• Use approximately uniform wall thicknesses throughout your designs.
• Keep walls thin - typically between 1/32" and 1/10". This allows for proper cooling and reduces cost by minimizing use of material. Thin walls also reduce problems with material shrinkage. Although some unevenness will occur due to shrinkage, walls as thick as 1/5" can be used. Keep wall thickness at least wall length / 50. Keep 90 deg walls under 0.25" high.
• Keep thickness of ejection pin surface wall at least .07".
• To strengthen parts, instead of using thicker walls, use additional structures such as ribs. Use fillets at the base of ribs.
• When using a rib make it about half the main wall thickness.
• Round corners and edges wherever possible.
• For easy release of the part from the mold, add a slight taper to the sides (typically ~ 2 deg) - especially for textured walls and walls higher than 0.25".
• Avoid undercuts that are impossible to remove from the mold.
• Lighter colors hide flow patterns better than dark colors.
• Where walls meet at a 90 angle, round inside and outside to at least .05" radius - sharper outside corners can create molding problems and sharper inside corners will increase tooling cost.
• Keep holes at least .015" from edges.

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Plastic Design International was started in 1977 in the short-run prototype R&D business. PDI is now one of the most effective Plastic Injection Molding production companies on the East Coast and an expert Mold Making manufacturer. Please contact us with any questions at 860-632-2001.

Four Injection Molding Variables

From Jake Tuczapski, Process Engineer, PDI

The successful plastic part is the combination of :

• Proper Part Design
• Material Selection
• Tool Design
• Optimized Process

Injection molding machines have a number of machine control options which affect the polymer as it moves from container to mold cavity. These include:

• Barrel Temperature
• Hydraulic Pressure
• Hydraulic Flow Rate
• Oil Temperature
• Function times
• Clamp Force

Process optimization and troubleshooting are easier when you understand how machine variables affect the four injection molding variables.

Plastic Temperature Plastic temperature or melt condition is determined by a combination of barrel temperatures, screw design, screw check valve design, screw rotation speed, back pressure and residence time. Plastic temperature should be checked using a calibrated pre-heated pyrometer placed into a purge puddle that was taken on cycle. Machine temperature controllers must be properly calibrated and tuned. Screw recovery time should be monitored for consistency

Plastic Flow Rate Plastic flow rate is measured in seconds from the start of injection until transfer to pack/hold at 95-99% full mold. This fill time is not the same as first stage timer setting. Fill time in combination with calculation of shot volume gives a volumetric flow rate which is a plastic variable measurement. Plastic flow rate determines plastic viscosity as it enters the mold cavity. As the plastic molecules flow, they untangle and become aligned. They take up less space and slide easily past one another thus reducing the viscosity of the polymer melt. Because of this unique and direct relationship of fill time to plastic viscosity, fill time must be maintained shot to shot and run to run.

Plastic Pressure Plastic pressure is defined as a measure of the amount of compression of the polymer in the mold cavity at the end of the molding cycle. It is necessary to control both the amount of polymer put into the mold and the amount of polymer maintained or held in the cavity until the gate has frozen. The key machine controls that determine plastic pressure are pack pressure, pack time, hold time. The best method of measuring plastic pressure in the molded part is to use cavity pressure transducers.

Plastic Cooling Rate/Time Plastic cooling rate and time will affect final part dimensions, part appearance and cycle time. The mold surface temperature affects part aesthetics and part performance by affecting the thickness of the oriented layer of plastic molecules. When the mold is filled with plastic, most of the heat content of the melt must be transferred to the mold cavity and ultimately away from the molding area. Some heat is lost by radiation but most is removed by forced convection through the cooling channels in the mold. Heat transfer can be optimized by having turbulent flow in all cooling channels, by keeping cooling channels free of scale that insulates, by directing coolant flow to the most needed area and by keeping the plastic against the cavity surface as long a practical. Compare “coolant temperature in”, versus “coolant temperature out” in each circuit to evaluate the heat removal performance. A difference of 4 degrees F or larger is undesirable and indicates poor rate of heat removal.

Plastic variable measurement is independent from machine variables and can be repeated on any injection molding machine.

I hope this information will help on your next project.

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Plastic Design International was started in 1977 in the short-run prototype R&D business. PDI is now one of the most effective Plastic Injection Molding production companies on the East Coast and an expert Mold Making manufacturer. Please contact us with any questions at 860-632-2001.

PlantStar

By David Mann – Facilities Team Leader, PDI Plastic Design International is upgrading to a new PlantStar production monitoring system. The new PlantStar system has been installed in all of the machines at PDI. It is now being used for job scheduling and tracking jobs for on-time delivery. Also, the Setup Technicians and the Material Team Members are using PlantStar to check for upcoming jobs so that they can prepare for them before they are due for production.

This new system has real-time tracking of machine and labor utilization, material usage and production efficiencies.

A very useful feature of this new system is that you can access a real-time visual snapshot of the delivery status of any job from any PDI computer.

Other features of the new PlantStar system are:

• Different part numbers in a family tool can now be tracked individually by part number.
• Production parts, machine downtime and the reasons for rejected parts are tracked and can be printed out by machine shift or job number.
• Images of good or rejected parts can be made available at any PDI computer.
• Setup, quality and operational documents can be accessed at any PDI computer.
• PlantStar data can be uploaded into our DTR system to adjust part and material quantities and usage.

This information will be accessible from anywhere on our corporate network or from any home computer that has access to our network.

Everyone at Plastic Design is very enthusiastic about the new PlantStar system that will make scheduling and monitoring production more efficient. ----------------------------------------------

Plastic Design International was started in 1977 in the short-run prototype R&D business. PDI is now one of the most effective Plastic Injection Molding production companies on the East Coast and an expert Mold Making manufacturer. Please contact us with any questions at 860-632-2001.

On Site Molding Advantages

By Susan Kenny, Business Unit Coordinator

In 1999, Plastic Design Inc. helped their customer, at the time Edwards Systems Technology (EST) - now GE Infrastructure (GE), set up an on site molding division. This was a big step for both companies.

They started with 4 all electric Niigata molding machines ranging from a 55 ton to a 200 ton press, a few molds and 3 materials. It was staffed with three shifts. Two people per shift with first shift having a third person to clean molds and make small repairs. Within a year Niigata was added to the cell (this time a 385 ton press), a couple of robots, a few more molds and a couple more materials.

The advantages of having the molding machines in the building were starting to shine through:

• Inventory levels were going down, no transportation costs for moving molded parts.
• Packaging costs were near nonexistent. Totes were replacing some of the corrugated boxes. Boxes were being reused over and over again.
• Molded parts were going straight to the floor, no more incoming inspections, quality measurements are done every two hours and all QA records are held on site. Parts were being handled much less.
• The on site molding division started taking over subassemblies which freed up space for EST/GE to start new product lines.

But these are the things we expected to happen when the project started. What were the advantages that weren’t right there in front of them when this idea came about? I don’t know about you but in the morning while I am riding to work I get in work mode. I am constantly thinking about how we can improve this or that. Now, normally when you have an idea on a part or project that is sourced to you, you have to email or call and send prints and give them time to look at what you’re talking about and then wait for them to get back to you, by then the excitement is gone!

Let me give you a couple of for instances. An Engineer with an idea or need comes down. We put the mold on the bench, open it up, look at a part, look at the mold and solve the problem or come up with an idea of how to make a change or improvement that needs to be made. Brainstorming time cut way down. No leaving messages and waiting to hear back!

Another for instance, the end user for a part doesn’t think the packaging is user friendly. That person sees me in the hall and says hey, can you look at this for a minute? I go to their station find out what it is that they would like to change to make it more user friendly for them, then go talk to the supervisor of the line see what we can do to make it work for them. This instance it was that the box was too heavy, so we put fewer parts in the box.

You can see that people from all aspects of the company have input. Some people might not ever bring up an idea they have because they might not know who to go to or what could be done to fix it. But, they see me and they know I am the manager of the mold shop that their parts are coming from and they ask what if, or hey, can ya? After nine years, ninety plus part numbers, fifteen or so materials and adding 14 more people to the crew, we have formed a bond with our customer that in my opinion cannot be replaced! We work together as a team, we problem solve together. We find ways to save money together and we make each others jobs easier and less time consuming. Parts are not late; lines are not down because someone forgot to order. We are down the hall and to the right.

I asked a few of the people I work with everyday at GE to give me their opinion of having on site molding and the advantage of it, here is what they wrote:

I do like the fact that there is no middle man. I can get my parts when I need them and there is no need to wait around for some sort of confirmation if the parts have been shipped, or have to wait around for the buyers to get a hold of the suppliers to see what the situation is. I can pretty much just go down the hall and get it myself! :) -Tanya Thompson, Material Handler, GE Security

Having the molding on site has helped us reduce our inventory and better service/quality. PDI on site has been very accommodating and is greatly appreciated. - Deborah Bagley, Production Supervisor, GE Security

Having on site molding provides reduced inventory levels, lower cost products, quality parts, fast delivery, and a wonderful partnership - Les Archer, POURS

My opinion as a Manufacturing Engineer is that having the molding on site is great for quality and making engineering changes. The problems that occur usually can be fixed within 24 hrs and all of the support need is very close at hand. This makes great use of demand flow lines and excellent quality for products. - Wendy L Rolfe, Process and Manufacturing Engineer

Now, my opinions of the advantages of being an on site molder: The biggest advantage for us as an on site molder is that we learn a great deal about the parts we make for our customer, what the most important characteristics of the parts are that we are supplying. How these parts are assembled together, how parts function within the product. In my opinion if we were not right here being a part of their daily operations we would not have this advantage. We are right here by their side trying to make their job and our job easier and more efficient by taking out the waste in a process. Being an on site molder has given us such a clearer picture of what we need to do to stay on top by adding quality, service and convenience. I don’t think anyone ever thought of all the possible advantages in the very beginning. This is true teamwork with no star players. We work together to make quality parts! ----------------------------------------------

Plastic Design International was started in 1977 in the short-run prototype R&D business. PDI is now one of the most effective Plastic Injection Molding production companies on the East Coast and an expert Mold Making manufacturer. Please contact us with any questions at 860-632-2001.

PDI’s Continuous Improvement Initiative & Training

By Dan Gish, Director of Quality, PDI

The primary focus of the business for the past several years has been on building a “Better Mouse Trap”. Our Improvements to product Quality and Manufacturing throughput are a significant part of how we maintain our competitive edge. By placing the focus on individual jobs and determining what is critical to quality, as well as, identifying the opportunities we have to increase efficiency, are how we created this recipe for success.

PDI Management is dedicated to the continuous improvement initiative. They have invested greatly in the manufacturing facilities, equipment, and processes over the years. The focus now is on the Continuous Improvement of our work force through education and training.

A couple of months ago, at the Plastic Designs Connecticut Facility, a Certified Six Sigma Trainer was brought in to perform an overview for the Management personnel. Over the past 2 months this trainer has conducted two, Six Sigma for Plastic Injection Molders workshops.

“This Six Sigma concept is not ‘just’ about Statistical analysis of data; it is a mind set and a business motivator to maximize business success thru continuous improvement. This is the path we are continuing on.”

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Plastic Design International was started in 1977 in the short-run prototype R&D business. PDI is now one of the most effective Plastic Injection Molding production companies on the East Coast and an expert Mold Making manufacturer. Please contact us with any questions at 860-632-2001.

PDI Happenings - Smart Choices in Todays Economy

Smart Choices

By Steve Everett, Manufacturing Manager, PDI

At PDI, our management team sat down some time ago and developed a strategic plan. One large part of this plan was to invest in new equipment for our molding department. After months of research and testing we realized the smart thing to do was to upgrade to electric molding machines.

We were one of the first companies in CT to purchase an electric press using the Connecticut Energy Efficiency Fund. With the help of CL&P (our electricity supplier) and the supplier of the molding machines, we were able to begin purchasing machines that were more economical and could run with better accuracy than the older hydraulic machines of the past. The initial cost of the electric machines is higher than a new hydraulic machine, but CL&P offered a rebate program and we were able to use that money as a deposit on the new electric machine. Also, we would realize a savings of electricity which would virtually pay for the machine over time.

Here is an example of one job that PDI is able to run more efficiently due to utilizing electric presses. We had a mold that ran 4 days a week, 24 hours a day at a 21 second cycle, it needed an operator 100% of the time, ran in a 2 year old hydraulic machine and we were getting occasional quality dings for the parts. We moved this job to our new electric machine and with no changes to the mold we were able to drop the cycle to 18 seconds and eliminate the labor of inspecting each part reducing it to a quality check every 2 hours, so the parts now just need a conveyor and a box to run. After 6 months we had shipped to our customer with zero defects.

Today PDI proudly uses 14 electric molding machines. We have also invested in sprue pickers and boxing conveyors. We have focused on taking labor out of running our parts, making us globally competitive.

Another part of our strategic plan involved taking advantage of a program offered by CL&P where they replaced all of our factory lighting with “high effect” lighting. We also installed a high efficiency chiller system for our molding department, taking advantage of the 2008 CL&P energy program.

PDI continues to look ahead to the future and plan wisely. With the high cost of energy and the challenges with the economy we are making the smart choices to be sure we are here far into the future and will be able to give our customers the best value for their dollar.

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Plastic Design International was started in 1977 in the short-run prototype R&D business. PDI is now one of the most effective Plastic Injection Molding production companies on the East Coast and an expert Mold Making manufacturer. Please contact us with any questions at 860-632-2001.

Quality Capabilities

• ISO9001 Registered
• “PPAP” Program = APQP, PFMEA, Quality Control Plans, etc…
• First Article Inspection Report
• Statistical Process Control
• Capability Studies
• Process Validation Studies
• Fully documented inspection plans and procedures
• ERP System Software
• Job review, and process set-up controls
• Document control
• Continuous improvement program
• Corrective & Preventative Action System
• Non-Conforming Material/Tool control
• Documented shipping Instructions
• Calibration Control System
• Internal Auditing Program
• Our Quality Department is fully equipped with the latest measuring devices including:
• Coordinate Measuring Machine (CMM) & Optical Measuring Machine…
• Regulatory Compliance Program

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Plastic Design International was started in 1977 in the short-run prototype R&D business. PDI is now one of the most effective Plastic Injection Molding production companies on the East Coast and an expert Mold Making manufacturer. Please contact us with any questions at 860-632-2001.

Plastic Design Quality Management System

ISO 9001-2000 Registered: PDI has an established and maintained QMS that is driven by our continuous improvement initiative. Our commitment to best practices for improving the quality of our products, processes, and business partnerships are * what has made us an icon in our industry. *Or, what has made PDI / our business operations a success….

Product Realization: As a supplier of Automotive, Fire Safety, Security Systems and Defense Industry products, to name a few, we have adopted QS / TS Quality tools for our everyday operations. From the PPAP kick off of the Advanced Product Quality Planning meeting 1, with our customer participation to establish what is critical to quality, through to the customer part approval process.

Process Control: Plastic Design has proven systems for Validating and Sustaining our products and processes. These are the key to maintaining the Quality our customers demand. We have Manufacturing visibility and materials traceability throughout the organization. This is achieved by using ERP Software that is a comprehensive operations management, distribution, and financial management tool set. Maintaining and Monitoring is achieved through our comprehensive; operation sheets, production & quality work instructions, mold and machine maintenance, and surveillance auditing. All these processes enable us to consistency produce quality products.

Regulatory Compliance: Global regulatory compliance is a necessary part of our business environment. PDI operations comply with the RoHS directives. We maintain an internal compliance system for Certificates of Compliance, RoHS and WEEE Compliance, and Material Composition Declarations IPC 1752-1.

Supply Chain Management: Development of suppliers is a critical aspect of achieving a consistent product. The foundation of any quality product starts with the quality materials going into it. ----------------------------------------------

Plastic Design International was started in 1977 in the short-run prototype R&D business. PDI is now one of the most effective Plastic Injection Molding production companies on the East Coast and an expert Mold Making manufacturer. Please contact us with any questions at 860-632-2001.

Mold Making Capabilities

Mold Making Capabilities

Our experienced tooling department personnel use their decades of combined experience to ensure the most precise tooling results available. For plastic injection tooling and prototyping applications, we meet your quality demands as well as those of your customers.

• Prototype & Multi-Cavity High Production Tools
• Domestic Tooling
• Asian Tooling
• Proficient and Highly Skilled Tool Design
• Hydraulic Core pulls, cam activated, unscrewing
• 3D Machining / CNC
• EDM
• Quick Turn-around Mold Changes
• Mold Sampling and Evaluation
• Production support/maintenance
• Engineering changes – design & implementation
• Innovative fixturing
• Solidworks

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Plastic Design International was started in 1977 in the short-run prototype R&D business. PDI is now one of the most effective Plastic Injection Molding production companies on the East Coast and an expert Mold Making manufacturer. Please contact us with any questions at 860-632-2001.

Plastic Injection Molding Capabilities

Our experienced tooling department personnel use their decades of combined experience to ensure the most precise tooling results available. For plastic injection tooling and prototyping applications, we meet your quality demands as well as those of your customers.

• Prototype & Multi-Cavity High Production Tools
• Domestic Tooling
• Asian Tooling
• Proficient and Highly Skilled Tool Design
• Hydraulic Core pulls, cam activated, unscrewing
• 3D Machining / CNC
• EDM
• Quick Turn-around Mold Changes
• Mold Sampling and Evaluation
• Production support/maintenance
• Engineering changes – design & implementation
• Innovative fixturing
• Solidworks

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Plastic Design International was started in 1977 in the short-run prototype R&D business. PDI is now one of the most effective Plastic Injection Molding production companies on the East Coast and an expert Mold Making manufacturer. Please contact us with any questions at 860-632-2001.

Bringing Innovation to Plastic Applications

Plastic Design International (PDI) has been providing custom plastic injection molding solutions for over 30 years for companies whose plastic products and components require critical tolerances and exacting specifications. Our team of experts works closely with each customer, focusing on their unique needs, to find the global plastic solution that is the best match.

We exceed our customer’s expectations every time by:

• Providing high-quality molded products: Plastic Injection Molding Capabilities
• Creating mutually beneficial partnerships with our customers and suppliers.
• Providing innovative, customized solutions for our customers’ plastic needs: Mold Making Capabilities
• Keeping abreast of the latest technological innovations.
• Utilizing best-in-class manufacturing practices: Plastic Designs Quality Management

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Plastic Design International was started in 1977 in the short-run prototype R&D business. PDI is now one of the most effective Plastic Injection Molding production companies on the East Coast and an expert Mold Making manufacturer. Please contact us with any questions at 860-632-2001.