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Machining Acetal Shapes

Highly precise acetal parts in a variety of sizes and complexities can be manufactured economically through machining. In the world of Engineering Plastics, Acetal (POM) stock shapes are considered to be some of the easiest to machine. On a scale of 1-10 with 1 being the easiest, many manufacturers place acetal at a 1, compared to a PBI which is often seen as a 10. In fact, machine shops that traditionally make metal parts find they can machine acetal using the same primary tools used for most of the metals they work with. As with any material, there are some good guidelines that can help ensure your success.

Best General Practices for Machining Parts from Acetal (POM) Engineering plastic and Potential Pitfalls of Machining Thermoplastic Shapes

We love engineering plastics! So we are always touting the many benefits of replacing plastics with metals. But this does not mean they are perfect in every way in every situation. There are some differences between plastics and metals that can trip you up when machining. But once you know the potential problems of machining acetal stock shapes machining them can become as easy as the metals machine shops are used to working with now.

Watch out for the heat! As a general rule keep in mind that, due to heat, thermoplastics expansion can be up to 10X greater than metals. Thermoplastics also hold heat longer than metals. Acetal is a thermoplastic material and has a lower thermal conductive aspect than most of the metals it is used to replace. Heat may not be an issue for metals but in the case of an engineering plastic shape from acetal heat build up from machining needs to be monitored and taken into account. Thermoplastics are more elastic than metals. So in general, heat buildup during the machining process can potentially lead to thermal expansion which can distort acetal parts.

If this leaves you concerned about machining plastics, not to worry! Plastics like acetal have numerous benefits that often outweigh the challenges of heat buildup and once you understand how to work with acetal you can easily machine consistently accurate, detailed high quality parts that your customers will be happy with. Be mindful of heat buildup, but also know that acetal does not typically require a coolant (except when drilling or threading). Sawing and machining can usually be set up to minimize heat buildup. (See the table below for Quadrant Engineering Plastics general recommendations for tools and speeds.)

  1. If cooling is used on acetal, compressed air is the standard method. The great thing is this has two benefits. The air cools the part and it keeps chips blown out of the way and keeps the heat built up in the chips off of the part or tools where it can add to any heat buildup. Other options include spray mists and non-aromatic, water soluble coolants.
  2. Sharper tools = Less friction = Less heat. To help reduce heat buildup use extremely sharp cutting tools.
  3. Chipping. Acetal creates chips when being machined so plan for removal of chips as you machine. Removing chips is very important in deep hole drilling. As the chips add to the heat, hole walls can heat to the melting point and clog the drill.
  4. Pieces may be flexible. Make sure the acetal is supported in a way that the material is not distorted, bent, twisted or allowed to deflect away from the tool.
  5. Make sure machining equipment is running as smoothly as possible, reduce any vibration to help aid in accuracy and part quality.
  6. Acetal shapes can be clamped but be aware of how tight.
  7. Choose the right blade for the job. Start by asking yourself what the end product is going to be.
    1. Band saws are good choice for a support groove and for cutting acetal rod and tube. Heat gets dissipated over the long blade.
    2. Circular saws are a good choice for cutting acetal sheet or blocks that have straight edges. Watch the feed speed (most acetal manufacturers have a recommendation).
  8. Choose the right tool for the job too
    1. Opt for positive tool geometries with ground peripheries
    2. For best tool life use carbide tools with ground top surfaces
  9. Is post machining annealing needed? See our previous blog post on this topic.
  10. Choose a machining cycle that will allow for evacuation of the chips from holes and cutting surfaces. For example, when drilling holes choose a cycle that allows drill to ‘peck’ or withdraw at certain points to draw chips back out of the hole.

The following tables are a good starting point for how to set up machining of acetal materials. The information comes two US manufacturers of acetal materials – Quadrant Engineering Plastics and Engineer Plastics provide guidelines for machining the acetal materials they produce. Depending on the manufacturer acetal materials may go through a stress relieving (annealing process) as part of their manufacturing. This helps to ensure the highest possible consistent quality of materials. Testing and consulting with your local tkEP representative on manufacturer recommendations is always a good way to help prevent machining problems. tkEP representatives not only have a broad range of industry experience, many have worked hands on in the industry, and all tkEP representatives attend manufacturer training so we stay on top of current products and how to work them.

 

As you can see each manufacturer has their own insights into how acetal should be sawn, milled, drilled, or turned. Their are also some pretty broad ranges when it comes to the numbers they provide. This is because these are truly general guidelines that cover the broad range of acetal shapes. Acetal shapes can be acetal homopolymers, acetal copolymer. In addition there are filled acetals and unfilled acetals. Add that to other variations including thickness and size plus environment and it is easy to see that testing for individual applications is necessary.

To read more about acetal plastic shapes check out our online catalog. We have product information as well as a full range of shapes, sizes, and grades of acetal. Read More… For more detailed information on machining from Quadrant EPP and Ensinger Engineering Plastics we’ve included links to pdf files of their machining guides. In these guides you’ll find data for acetals as well as a broad range of other machinable engineering plastics. Last but not least, don’t forget about your friendly local tkEP representative. We are always happy to assist you with finding the right engineered plastics solution for your application. Contact us today 877.246.7700. this one number will put you in contact with your local tkEP branch, or send us a note.

Quadrant Engineering Plastics Machinist Handbook

Ensinger Engineering Plastics Machinist Guide

Living Safety Is the Focus tkEP SHIELD Program

shieldThe SHIELD Safety program has been in place for all of 2016 with training, games, quizzes and contests to keep all thyssenkrupp Engineered Plastics employees involved and engaged at work and at home. SHIELD stands for Safety and Health Initiatives for Employees to Live Daily and with that in mind Safety should not be something we think about when an accident happens, but a conscience change to think about life choices and the task at hand BEFORE we do it.

I recently asked the Safety leaders in each branch to summarize what SHIELD has meant to employees, their families and how they are looking at safety differently.

  • The team in Grand Prairie Texas said “We look out for one another to catch any slip, trip or fall hazards at work and we push each other to maintain a healthy lifestyle by joining the tkactive program, walking at lunch or participating in 5K runs on the weekends. We are thankful for this program to remind us how important it is to maintain a safe and healthy lifestyle and it motivates us to be better every day”.
  • The Yonkers New York group reported “The pre-shift safety meetings have allowed everyone to be involved in setting a positive tone for all the warehouse associates both at home and work. Everyone has a turn to choose a topic of the day and present it to the team. There was an occasion when our topic of the day directly impacted an occurrence at an employee’s home. The topic was fire extinguishers so the employee went home and discussed this with his family. The following day there was a fire alarm in his apartment building and his 8 year old son knew exactly what steps to take to ensure the safety of his family. This definitely highlights the fact that safety does not only apply to the workplace, safety is even more important at home”.
  • In Riverview Florida “Safety isn’t just wearing a hard hat or making sure your shoes are tied, we don’t only focus on being safe but making sure our surroundings are 100% safe. It doesn’t matter if we are in the office calling customers or in the warehouse building skids. SHIELD has taught us not only to be safe at work but also practice safety at home. ‘When you gamble with safety, you bet your life’”.
  • Auburn Hills Michigan responded “Our employees continue to search for anything that could injure someone and report and correct it as soon as possible. We have never had a recordable injury at this facility and we all want to go home daily with the same amount of blood, skin and bones we arrived with”.
  • Earth City Missouri says “SHIELD means having safety in the forefront at all times. At work we always stress safety and while training a new warehouse associate from another branch we told him to take his time and work within his limits and don’t let others try to influence him to go beyond, especially if unsafe. We recently updated our cut resistant gloves and signage for changing the saw blades. One employee states he recently got his motorcycle license after completing the safety course and he said the one thing stressed was All the Gear All the Time and being prepared for all riding conditions. This is good information for any situation at work or home.”
  • Columbus OH had input from everyone “SHIELD is a reminder at work that our Safety, whether it is wearing steel toe boots or sunscreen impacts everyone including our families. A safe and healthy personal life can work in conjunction with a safe and healthy professional life. This has impacted me by making smart decisions that will affect my future in a positive way. When you work for a company that stresses safety in the work environment it becomes an automatic thinking process when you are outside the work place. SHIELD is inspiration – inspiring us to find new and creative ways to stay healthy and stay safe. SHIELD is responsibility -learning from mistakes and embracing them. SHIELD has become part of our culture.”
  • Lancaster PA “has implemented the SHIELD process into the culture of our workplace. It has shaped how we see the warehouse that we work in enabling us to see potential safety risks and correct them before they become issues. For example when freight came into our facility damaged with no bands we immediately restacked it as we sorted the damaged material for the claim. When putting skids in the racks, if boards or planks are broken off or hanging we remove them at that time so they don’t become a problem in the future causing material to fall. At home whether cooking, enjoying nature or sports, cleaning or working in the garage this conscious thought process keeps family members safe and healthy. SHIELD is a transformative process that first changes ones conscious perspective and then changes one’s world, creating leaders in health and safety.”

As the Operations Manager I can give our employees tools and support but I can’t wave the magic want and change the culture. The real change to embrace Safety and Health as part of our culture is owned by the employees. SHIELD has become part of our daily lives at work and home based on the descriptive responses I received. If our employees are active and healthy and feel safe and confident at work the possibilities are endless!


Contest Winners! Team Yonkers got top honors and lunch for the entire team for their entry – “What SHIELD Means to Us and Our Families.” Congratulations and thank you for sharing your story of how the tkEP SHIELD program made a difference and showing us how we all win when we put safety first.

 

Photo-Gestewitz-T-DSC_0291Theresa Gestewitz

Operations Manager
thyssenkrupp Engineered Plastics

About Theresa Gestewitz –
Ms. Gestewitz began her career with ThyssenKrupp Materials NA AIN Plastics Division 20 years ago. Her first role was Buyer for the Lancaster, PA facility. She has also held additional positions as Office Manager, Corporate Buyer, and Plant Manager. She assumed her Safety Leadership role in 2010.