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EPP’s Alex Curtiss featured in MDT Magazine

Alex Curtiss

Alex Curtiss President and CEO, Engineered Plastic Products Corporation

It is natural for a company that makes highly sensitive medical devices to turn to a trusted vendor to make its components. But if those components are made of plastic and that vendor is a metal machinist, that can be a huge mistake.

A company that specializes in only machined plastic parts not only brings expertise in dealing with plastics to the table, but can help avoid problems that might arise from contamination or simply not understanding the subtle differences between working with plastic, as opposed to metal parts.

Take the case of a medical analytics company that turned to a metal machinist to make a plastic component. The part had precisely made holes that needed to contain a small ball to measure gas levels. If working properly, the ball would float in the instrument. Unfortunately, even after passing initial inspections, these parts sometimes failed after two to three weeks in the field. The ball would no longer rise. The manufacturer thought it was a problem with static—a reasonable assumption, but one that proved wrong. The real problem became apparent after putting the piece under a microscope. There were tiny cracks inside the holes, not visible to the naked eye. The cracks were due to crazing, a degradation caused by cutting oils. That is not an uncommon problem when metal machining equipment is used to create plastic parts.

Components for medical diagnostic equipment
Components for medical diagnostic equipment

Metal parts, unlike plastic ones, typically require the use of oil-based cutting fluids. And no matter how conscientious the metal machinist is, it is nearly impossible to clean every bit of oil from a machine before using it to make a plastic part. Because of this, equipment used to manufacture metal parts, even if used for metal only, can occasionally contaminate plastic parts with those oil-based cutting fluids. Many plastics are highly sensitive to petroleum-based cutting fluids and will degrade if they come into contact with them. Also, many plastics are hydroscopic and will absorb the cutting oils. The result is a part that may pass initial inspections, but will degrade over time and fail in the field.

It is not just cleaning oils off a machine that is difficult for a metal machinist, but also clearing every tiny metal fragment that may remain on a machine used to make metal parts. If the plastic material being machined is soft, residual metal fragments can become embedded in the plastic machined parts. Again, the metal fragment may not cause a problem initially, but over time it can cause the plastic to degrade and stop performing properly.

Problems can also arise in something as simple as how a metal machinist holds a plastic part. With plastic machined parts, the plastic is usually held with vices. Machinists who don’t specialize in plastic have a tendency to hold the plastic the same way they do metal—but this can be too tight for a plastic. As a consequence, when a drill goes into the plastic, the material flexes a bit, which can put stresses on the part that might not surface until later. A plastics machining company would know that, and be able to prevent that from happening. It is a subtle difference in manufacturing, but one that can turn into a huge problem down the road.

Of course, a plastics expert should be more knowledgeable than a metal machinist about the variety of plastics materials available and what uses they’re best suited for. This level of knowledge is especially important in fields like medical device technology, where manufacturers often use plastics that are less common than those used for other purposes. A plastics expert can help designers and manufacturers sort through materials according to factors such as sensitivity to humidity, abrasion resistance and thermo-sensitivity.

A company that specializes in only machined plastic parts not only brings expertise in dealing with plastics to the table, but can help avoid problems that might arise from contamination or simply not understanding the subtle differences between working with plastic, as opposed to metal parts.
A company that specializes in only machined plastic parts not only brings expertise in dealing with plastics to the table, but can help avoid problems that might arise from contamination or simply not understanding the subtle differences between working with plastic, as opposed to metal parts.

Sourcing is another important consideration. A metal machinist will most likely get their plastics from a distributor whose materials may come from a variety of sources. They may be able to provide certification, for example, that all the materials they are using are nylon rods, but they may not know the source of those rods. A plastics specialist, on the other hand, should be able to tell you not only what mill the material came from, but also the lot number. If there is ever a problem, they can easily trace the material back to its original source. There is a level of accountability you may not get from a metal machinist.

Of course, not all plastic machining companies are alike. The best for your job is one that is familiar with each machining process you need for your medical device application, as well as with the specific plastic material you will be using. The company should have access to up-to-date information and be willing to share it through property charts or plastic material handbooks.  They also should be ISO Certified, use documented SPC (statistical process control) procedures and own the proper inspection equipment such as CMM (coordinate measuring machine) or video inspection systems. These certifications and systems will help ensure that you receive the highest quality medical device for the lowest cost, with the fewest possible errors the first time around.

The final consideration in this is cost. Surprisingly, using a plastics expert may actually save money.  Plastics machining companies deal with plastic parts all day long. Their expertise means they can often perform the job more efficiently than the typical metal machinist. But most important, the lower risk of contamination when dealing with a plastic machinist means that medical device parts not only have a higher chance of passing inspection, but a much lower chance of failing down the road. That is important in any industry, but even more so when someone’s health is on the line.

This article appeared in the March 2016 print edition of MDT.

Plastic Machining: Design Guide for Plastic Parts

How to use the Plastic Design Guide

  1. Refer to the Design Considerations at the bottom of this page. Consider whether each item on the checklist is a factor in the application or affects performance requirements for the component design.
  2. Select the categories that have the greatest affect on your application.
  3. Review the materials in the Free Plastic Properties Handbook and make a list of possible material candidates.
  4. Contact our technical support to discuss options or ask additional questions.

Custom Plastic Machined Components

Plastic Machining Design Considerations

  • Thermosensitivity – tolerance can change in different temperature conditions
  • Sensitivity to humidity and hygroscopic absorption affects tolerance
  • Sensitivity to chemicals and oils
  • Notch sensitive corners and square ID’s
  • Tolerances
  • High loads
  • High impact
  • Fatigue loading or cycle loading requires consideration of flexing, deflecting, and compression
  • Temperature – max/min extent of time
  • Electrical considerations such as insulating properties
  • Wear resistance or abrasion resistance
  • Dimensional shape retention (load, cold flow, temperature)
  • Regulatory requirements (FDA, UL, etc.)
  • Appearance (color, texture)
  • Optical requirements
  • Outdoor use

Now that you’ve identified the important factors in your application, evaluate material specs in the Plastic Properties Handbook and select your material!

Plastic Machining: Selecting a Plastic Machining Vendor- Looking for the Best

Selection of a truly qualified plastic machining vendor is extremely important in today’s business environment. The time it takes to ask the right questions will pay big dividends – helping you obtain high quality machined plastic parts. And even though the rules for service and quality seem to be continually evolving, getting the best part at the lowest possible price is still the golden rule of purchasing.

If you’re looking for a plastic machining supplier, don’t settle for anything less than the best. Request a Quote from EPP Corporation today.

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Plastic Machining: Selecting a Vendor Looking at Quality & Price

Quality, of course, is directly related to price. Make sure the vendors you interview can provide the highest quality part at the lowest price. Plastic machining vendors can keep errors to a minimum if they are highly process driven, are ISO Certified, use documented SPC procedures, and own the proper inspection equipment such as CMM or video inspection systems. The plastic machining vendor with the fewest errors will produce the highest quality and at the lowest cost.

Make sure the supplier is familiar with each machining process you need for your application, as well as with the specific plastic material you will be using. Experience, more than anything else, will help make sure a supplier offers you the most cost-effective part with the best quality.

If you’d like to see how a process driven, high quality machining vendor compares to your current supplier, Request a Quote from EPP Corporation.

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Plastic Machining: Selecting a Plastic Machining Vendor- Equipment

Ask about the type of equipment the potential plastic machining vendor uses. The well-equipped plastic machining vendor will look pretty much like a metal machining shop, but the true plastic machining specialist will have equipment that has been adjusted or re-built expressly for machining plastic material. The right equipment will machine plastic using the correct speeds, feeds and tooling, and won’t pose the threat of contamination faced when metal-machining equipment is utilized. The right equipment will also insure higher quality plastic machined parts with better finishes and less chance of chips, burrs and other imperfections.

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Plastic Machining: Selecting a Plastic Machining Vendor- Purchasing Practices

Just as a metal machine shop is unlikely to have the material knowledge you need, neither are they going to be able to purchase plastics in large enough quantities to provide you with the best price.

Likewise, find out if the plastic machining vendor candidates you are considering can purchase materials directly from material manufacturer. If they rely on plastic distributors for materials, make sure their vendors are up on the latest material technology. Plastic technology is constantly changing with new materials introduced all the time.

One of your goals should be to make sure that your plastic machining firm’s materials purchasing practices are as good as yours.

To find out more about EPP Corporation’s purchasing practices, contact us today!

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Plastic Machining: Selecting The Right Plastic Machining Vendor For Your Custom Plastic Machined Parts

Not all plastic machining vendors are equipped to offer all parts. Others may not be able to give you the best prices. The following guidelines can help you locate a fully-qualified, cost effective plastic machining specialist for all your plastic machined components:

  1. Material Knowledge
  2. Purchasing Practices
  3. Equipment
  4. Quality and Price
  5. Looking For the Best

Be sure to ask potential plastic machined parts vendors how they comply with these guidelines.

If you have a need for plastic machined components, request a quote!

Plastic Machining: Custom Plastic Components- Molding vs. Machining

With every project that includes plastic components, you will need to answer the question, “Should I machine or mold this part?”

The two major factors needed to reach your conclusion are quantity of parts and level of dimensional tolerance. As a general rule, you should consider plastic machining when lower volumes are needed or tighter tolerances on the dimensions are needed – or both.

Quantity of parts is significant because of the tool cost of a molded part. If you are injection molding your part, the molding tool will typically cost several thousand dollars and tooling for complex parts can cost hundreds of thousands of dollars. Tool costs can make injection molding unfeasible for a low volume run.

Quantities between 100 and 1,000 – on some parts even up to 5,000 – are usually good candidates for conventional or milled plastic machining. Screw machining of plastics can be practical and cost effective from 500 pieces all the way up to 100,000 pieces or more.

Tolerance is a factor because plastic machined parts can typically be produced at a tighter tolerance than molded parts. Each plastic material behaves differently, but you can generally achieve tolerances +/- .005” for molded parts. Plastic machined parts can be produced +/- .001” or better depending on the material and design. This is why critically precise industries – like instrumentation, medical equipment, aerospace, fluid power, telecommunications, and many others – have turned to plastic machining for component needs.

One last advantage to plastic machining is flexibility of design. Once an injection mold has been produced, it can create only that design and any modification to the design requires expensive changes in the mold. Design changes to custom plastic machined parts are immediate and have virtually no impact on tooling costs.

Plastic Machining: Selecting a Plastic Machining Vendor- Material Knowledge

Quiz potential vendors on their knowledge of various materials and applications. Ask them to share the information they have from their material manufacturers. Do they have any property charts or plastic material handbooks to give you? Specialists in plastic machining should have a wealth of up-to-date information.

Material knowledge is a critical area. Good plastic machining firms must be willing to educate you before you finalize your choices, and help you find the best material for your application.

If you need assistance selecting a plastic material for your current project, EPP Corporation is happy to help! Contact us today!

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