The Secrets Behind Part-To-Part Molding

For many facilities, achieving quick part to part times are a struggle. After all, part to part is an absolute necessity if you intend to satisfy your customers and still maintain a solid profit margin. But what are the reasons so many companies fail to shut down a press, do a mold change and put good parts on the belt quickly? This article will define the part-to-part function, as well as provide information on how to convert from sluggish to successful in terms of job change events.
The first step to addressing your part-to-part approach is understanding what part-to-part is by definition. The term consists of 4 actions:

1. Planning- Quick mold changes require planning the event. Many companies think that fast mold changes are the result of fast-moving employees. This is a MYTH! SPEED KILLS.. The key to successful part-to-part events is doing all the thinking normally done during the mold change before the press ever shuts down. Think about NASCAR.. are pit stops planned when the car pulls up for service? Of course not! The following steps are planned long before the press is shut down:
• Clamps- will the clamp set up be different on the next mold? How can I prep clamps to speed up my change?
• Barrel Temperatures- Will there be a big change in barrel temperature? How will I need to prep the next material? What purge requirements are there, and how can I purge quickly and efficiently?
• Mold- are the thicknesses the same? Where is the mold? Where do I place my mold to improve hoist in-the-air time? Does the next mold need more or less hoses? Are the hot runner set ups similar? Will the valve gate set up change?

• Robot set up- Where is the end of arm? What is different about the new end of arm? Where should I put the EOAT to assure I can install it quickly?
These are just a few of the considerations you need to consider during the planning stage. Every plant is different, and you need to develop your own approach. Work with your mold change team to find ways to eliminate waste of motion.
2. Mold Change- After planning has been completed, the press is shut down according to the plan you developed regarding the incoming material, unless the same material will be used. Mold change time is referred to as “steel-to-steel”, but there are many factors that can affect the next stage, Start Up through poor steel to steel planning or performance. Here is a list of fundamental fails that often contribute to waiting to start events:

• Consistency- Good mold changes are thoroughly performed, and a completed mold change consists of all steps performed satisfactorily. The set-up team must inspect the results of their work to assure the press is ready to start. Failure to do so results in inconsistency, and this slows down the technician’s audit of the set up. It can literally force the technician to analyze every step the set-up crew performed. This literally leads to the mold change being completed a second time through inspection not actions.
• Temperature-Based Changes- Part of the planning stage requires an assessment of whether there will be major changes in Barrel, Mold and/ or hot runner temperatures. If so, plan these for the beginning! If the steel-to-steel event is complete, but start up is waiting on temperatures to rise or drop.. the steel-to-steel event failed! Verify ALL heats are working properly
• Mold Inspection/ Preparation- The first stage of mold inspection occurs during the planning stage. Mold components/ fitting/ safety straps, etc. are inspected for repairs needed prior to shut down. Second stage is inspecting and cleaning the mold prior to start up. Clean cavities and parting line, inspect greased areas to assure worn grease is removed, and all moving components are satisfactorily greased and functioning. Look for broken/ damaged/ poorly performing components. Dry cycle clamp, and verify low pressure close and die height. Verify core operation carefully!
• Water- Look for leaks! Check water line placement… dragging water lines lead to water clean up and down time. Water hook ups? VERIFY, VERIFY, VERIFY. Molds that overheat because water set up was incorrect lead to unplanned mold changes.
• Process- Learn how to verify the key variables of a loaded process! At the very least, verify temperatures, shot size, cutoff, hold, and back pressure to assure all are set correctly. Loading a process does not promise a safe process was loaded!

3. START UP- Technicians are the last line of defense! Poor start ups lead to molds being pulled, and unplanned mold changes. One of the best tools you have in your arsenal is the 5 M’s of molding audit process! The audit you perform on the results from the mold change are key to making your start up approach effective, with minimal scrap. Here is how using the 5 M’s at start up assure that the start up goes smooth, with minimal hiccups:
• Man- Before you start your audit, notify the supervisor you are ready for an operator. This assures that an op is available once the first parts hit the belt. You also want to make sure the area is ready for the operator! Packaging for new job should be in place, old pack should be gone from area, new labels replace the labels from the last job. Verify that automation for the new job is both in place and working properly.
• Mold- Verify mold is clean, and ready to mold parts. Verify hot runners, core operation, mold movement, valve gate operation. Purge through the mold to verify hot runner is clean, and valve gates are working properly. Look for mold damage or wear. Verify hot runner temperatures, and that all zones are up to temperature called out on set up.
• Machine- Verify press and robot programs are loaded. Verify the set points called out in the set-up section of this article. Verify all auxiliary equipment is in a ready to run state. Verify end of arm has been changed, and that the EOAT set up is correct..
• Material- Verify material is correct for new job. Verify barrel and mold temperatures are correct for material. Purge the press through thoroughly, and check purge puddle for signs of moisture.
• Method- Method is process! Verify that the process loaded matches the program loaded. Set Pack and Hold to zero when you fire your first shot. First shot (Fill Only) should be 95%-98% full. If all is satisfactory, start running the press. If parts are not acceptable by 3rd shot, look for something wrong!

Fast changeovers are easy to achieve if you follow the steps outlined. Remember that part to part times can be fast only if proper planning has been performed. Mold changes must be consistent and thorough. Start ups must be methodical, with care being taken to inspect mold changes. Once a change over proves itself repeated, start the press and enjoy the satisfaction of repeatability!

Plastic Injection Expert Network