When you perform color or material changes with your injection molding press or extruder, what does it cost you? If you’re not sure, that’s okay. You’d be surprised how many people never actually take the time to figure it out. So let’s take a closer look.
The resin and colorant used to go from one color to the next are the most obvious costs. Using commercial purging compounds can also contribute to the overall cost. A less obvious, but significant and incredibly costly part of the color change is the parts that are scrapped until the parts are “good.” These parts are consuming resin, colorant, labor and machine time.
Remember, you only get paid for the parts you sell. The parts that are scrapped are just that. Scrap. You should know the cost and time required to go from the last good part on one color to the first good part on the next. Good part to good part.
The most expensive part of this equation is often the most overlooked: the machine burden.
What does it cost to have the machine and the work cell? Consider the chiller, thermolater, robot, conveyor, blender, secondary, operator, maintenance, & electricity. Don’t kid yourself—if the machine is not running and producing good parts, it is costing you money. Lots of money. Machine burdens vary by tonnage but are commonly $100 per hour for smaller presses and several hundred dollars per hour for large tonnage setups.
The faster you can successfully change colors and materials the more profitable you will be.
Make sure you plan your changes ahead of time. Know how many shots are in the blender when you stop it for a color change. How many shots are in the screw and barrel? Be prepared for the change. Get the machine back into production as soon as possible. Get back to making money.
Finally, it’s crucial to perform a Cost Savings Analysis on each color change in order to calculate the total cost. How much purge material did you use? How much resin and colorant did you use? How many parts did you scrap before they were “good”? Most importantly, how long was the machine down? What is the hourly machine burden for this machine? This is the cost of your purge. Knowing this cost is the key to making informed decisions to optimize this process. Once you know that, you’ll be amazed at your results.
Learn how to reduce machine downtime with five quick purging compound tips for your injection molding application.