How to select a modular cutting tool system

Modern Machine Shop, Jan, 1991 by Rick Neigoot

A modular cutting tool system will yield outstanding results provided it receives the discipline needed to make it work.

JIT, FMS, modular tooling, quick-change tools--these arc terms that we see and hear often today. What does it all mean and, more importantly, do you need it?

The one word that describes the very essence of the manufacturing environment today is change. Changes are taking place in the workforce, labor relations, the global economy and competition from the Far East and Europe. There is a stronger push for lower costs, higher output, better quality, reduced cycle times and increased flexibility. One method of preparing for and meeting these changes is the application of modular tooling--specifically, quick-change tooling. All quick-change tools are modular, however, not all modular tools are quick-change. The following information is designed to help in the decision-making process for the application of a quick-change cutting tool system. Note that here we are talking about cutting tool systems, not modular fixturing.

If we refer to the graph showing the total number of CNC machines projected through the year 2000, we can see that CNC machining is becoming more and more of a factor. We can also see that CNC lathes outnumber CNC machining centers almost two to one. Since the mid-1980s, there has been a new player in the game--the mill/turn center, or CNC lathe, with live spindle capability. The graph in Figure 2 [omitted] reflects the projected sales of live spindle lathe CNC machines. These machines are now available with higher horsepower, allowing more metal removal with rotating tools than ever before.

Just-In-Time

One buzz word that means something to all industry, regardless of the manufacturing environment, is JIT, or just-in-time manufacturing. This is an area into which all phases of manufacturing are forced, both by customers and overall inventory costs for finished goods. Part run quantities become lower and the cost of finished goods becomes more important than ever. This is also the area that should be the main focus for the successful application of quick-change cutting tools.

Figure 3 [omitted] describes an average time-scale in a typical manufacturing process. Percentages are shown indicating the amount of time spent on machine maintenance (both scheduled and unscheduled), part changing, setup, part measuring and metal-cutting. Your percentages may differ from those shown. The very best implementation of quick-change tooling should help you steal a portion of time from each of the nonmachining areas and add that time to the metalcutting process. This is the only way to effectively gain additional income from the process of manufacturing workpieces.

The best place to start is to examine your application areas. Time, effort and money have already been spent purchasing the best-suited cutting tools for your machining needs. Quick-change tooling should do more than simply increase metal removal rates. If we are to believe Figure 4 [omitted], then we must evaluate how the addition of quick-change tooling can transfer some of the nonmachining time to the business of making chips.

The basic concept of all quick-change tooling is the same. It is the application of a basic clamping unit to a turret position on your machine tool that remains fixed in that position. Into that clamping unit can be clamped any variety of cutting units (cutting tool carriers) to accomplish the metalcutting process. This modular system should be at least as rigid as conventional tools and have the ability to be changed quickly and easily. If the system meets that criteria, considerable time will be saved during tooling changes from batch to batch, compared to the time spent changing conventional tools.

Time-Savers

Another (and perhaps the most important) area in which time should be saved is in tool setting and part measuring on critical finished dimensions. If the coupling mechanism is extremely accurate, this is accomplished by an off-machine premeasuring method. Cutting units, complete with inserts, are measured from a master unit (any designated cutting unit) to determine differences in the X axis (the axis used to machine the diameter of a workpiece) and Z axis (the axis used to machine workpiece lengths). The master is used to set the machine in that turret position one time only and future tool changes in that position are accomplished by changing cutting units and entering the premeasured differences from the original master cutting unit into the machine control's offset values. By using this method, the machine's CNC control always knows where the cutting point is located. If the machine's control knows where the cutting point is, the dimension being machined is always correct, eliminating the operator's cut and measure procedure used with conventional tools. A great deal of time can be moved from this area to the machining process, and, more importantly, finished sizes are right the first time, every time.

Two additional areas in the machine tool life cycle can be viewed as potential time-savers. The first is the avoidance of unscheduled machine maintenance resulting from machine wrecks. If the cutting point locations are accurate, wrecks related to poor setup or wrong tool locations should be eliminated. The fact that cutting units are changed, instead of worn inserts being indexed on the machine, allows the operator to easily inspect the cutting tool pockets for damage, reducing insert breakage due to worn pockets, broken shims and hardware.