Multitask machining needs industrial-strength CAM.
As the name suggests, MTM machines do more than a single machining task in a single setup. A single-task machine is a basic mill or lathe. In the old days, most parts required multiple setups on multiple machines. When you take a close look at the labor costs in this style of manufacturing, it's surprising how much labor is involved with each setup, with each part transfer, and with the inspections required at each step. Just moving and storing incomplete parts around the floor is expensive. Machine time is not the only expense. To be accurate, you have to factor in a significant cost of scrapped parts. Each setup introduces an in creased risk of human error and of scrapped parts. Of course, this invariably occurs and is detected in the last operation.
MTM machines range from simple to complex. The simplest MTM is a lathe with a sub-spindle--able to perform work on two sides of a part, the equivalent of two setups. But this part transfer is automatic, and the alignment between setups is as good as it gets. You can add live tooling, B and C rotary axes, a Y-axis, and a second turret to support two tools cutting at the same time. This style of MTM is called a twin turn. Instead of turrets, some MTM machines use a mill-style automatic tool changer (ATC) with a B-axis on the tool spindle. As these machines grow in size and horsepower they look more like large five-axis mills, not lathes, but they still combine and perform well on both types of machining. The Mazak Integrex machines are a good example of this kind of CNC. MTMs don't stop with two tools cutting on two spindles. Models can be found with three, four, or more tools cutting simultaneously, as they transfer parts through any number of part spindles. Some popular configurations use Swiss-style sliding headstocks, and sliding gang-tool changers. Others include programmable steady rests, programmable tailstocks, bar feeders, bar loaders, part catchers, part grippers, robots, etc. The range of MTM machine model configurations is incredible.
The goal of an MTM machine is to produce a finished part in a single setup. This single setup and this single part program are both more involved than part programs and setups on single task machines. But there is only one of each. MTM machines themselves are more expensive than single task machines. But they eliminate multiple setups. They eliminate part transfers and part handling. They eliminate the human errors associated with multiple setups. They eliminate the out-of-tolerance error accumulation of multiple setups. They eliminate multiple inspections. They occupy less floor space. They cut parts faster from multiple tools cutting at the same time. Material goes in, accurate finished parts come out. It's amazing what MTM machines can do. Not only that, but they dramatically reduce the labor cost of a part.
There is a direct relationship between the cost of programming and setup, and the minimum number of parts that can be economically run for a job. As the programming and setup costs increase, you need bigger job runs to amortize these higher costs. In the early days of MTM machines, they were commonly viewed as high-volume machines because of these high programming and setup costs.
This is the lead-in for talking about CAM software--because nobody should be programming these machines manually.
Multiple tools cutting at the same time are impossible to organize and optimize without good CAM software. You can't see collisions, incorrect toolpath, or interference issues looking at G-code. You can't see the time-based overlap of multiple flows. You can't edit or splice together G-code without an unacceptably high risk of human error. The right CAM software eliminates these issues and will reduce programming and setup costs to the point that MTM machines can be quite cost effective on short-run parts.
CAM software is the tool that makes or breaks the case for the MTM machine's business. Programming time is the first issue. You can't cut parts until the part program is complete. Setup and program prove-out come next and they are hugely expensive, as they require machine time. Programming time might be cost at $50/hour while machine time might be cost at $500/hour. You really don't want to waste machine time. You don't want to create or edit part programs on the machine. You don't want to take programming errors to the machine. And you really, really, don't want to let a programming error crash the machine, adding repair costs and down time to this "not-cutting good parts" time.
Let me describe how GibbsCAM provides powerful yet easy-to-use solutions to MTM programming problems. GibbsCAM MTM is customized for each specific machine configuration you have. When you select the machine to program, GibbsCAM knows everything there is to know about that specific machine; from axes travel limits, feed and speed limits, tools and tool groups, to every option this machine is configured with, because GibbsCAM starts with a customized machine definition. Your machine is exactly represented in custom software, allowing GibbsCAM to directly program all functionality, period. As you define your desired toolpaths using GibbsCAM machining functions, you watch all the tools cut on the screen synchronized in time, verifying the correctness of the detailed machining and operation order. Each simultaneously moving tool has its own "program," called a "flow." GibbsCAM displays and programs as many flows as your machine has. GibbsCAM has a time calculated multi-flow display (the Sync Manager), showing the time-based overlap of the various operations. Adding synchs is a mouse click. Reorganizing tools and operation order is "drag and drop," graphically interactive. The software also offers a custom selection of utility operations for each machine, providing specific non-cutting operations to be integrated into your part program. These include load material, unload part, sub-spindle in, sub-spindle return, parts catcher in/out, tailstock in/out, position steady rests, shift the part, park a tool, stop the machine, and a variety of specials for machines needing additional user-mode control.
When the part program is complete, you may choose to use GibbsCAM Machine Simulation to test the setup. This allows you to enter all offset data for the tools, tooling, and the part, and to watch the machine run with automatic collision detection. The machine model is a detailed and accurate representation of your exact machine. If a programming error has been made, you catch it before going out to the machine.
The last step is post processing. Post processors change the pretty toolpath animations on the screen into G-code for your exact machine. GibbsCAM MTM post processors are custom built for you by professional post processor developers. Do-it-yourself kits just don't cut it at this level of CAM/CNC sophistication. General-purpose one-size-fits-all post processors are not much better. You want a G-code program that will cut exactly the part program you have created and proven out. You want a G-code program for exactly your machine configuration, taking every detail into account. You do not want to be editing/merging G-code in any way. If you find yourself doing any of this, it's an indication that you are doing work that your CAM system should have done for you.
CAM software is a critical tool for the successful utilization of MTM machines. Make sure you get the most out of your MTM machine. Make sure you pick a good CAM system. Gibbs & Associates, www.rsleads.com/707tp-155
By Bill Gibbs, Founder/President, Gibbs and Associates
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|Title Annotation:||software solutions|
|Publication:||Tooling & Production|
|Date:||Jul 1, 2007|
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