Conventional Method of Tool Supply Systems

In the conventional method of tool changing in which the machine tool will have to stop for the complete tool magazine refurbishing along with new tools or for single tool exchange. Such types of storage units as drums, chains, discs and other forms are employed. There is a limit to the maximum number of tools available at the machine tool in this form. The limit may be of the order of 120 or so. Refurbishing of the entire tool magazine is normally done during the start of the shift. Care has to be taken to see that the tools loaded complete all the machining till the end of the scheduled period. In an automated system, this would call for large machine stoppage time for complete tool exchange as well as make the cost of tools in the system prohibitive. There is no secondary tool storage system available close to the machine tool.

In the second case, the traditional system is modified slightly. The tool magazine is split into two or more smaller magazines, so that the machine tool can be running while one of the tool magazines is being replenished. In cases where a number of tools are to be augmented, more than two tool drums (or discs) have also been used as in the Yamazaki Minnokamo factory Japan. Sometimes the second and subsequent tool drums (discs or chains) carry special tooling required less often for special jobs. One of the disadvantages is that if a job requires more tools than can be accommodated in the small capacity of the drum or disc, more frequent disc transfers would be required. This would make the tool change time small, but would increase the cost of tools in the system to higher than in the previous case. Hence this method is not widely practised.

In the third system, an entire tool magazine is swapped for replenishment so that tool resharpening and replacement into the magazine can be done in the tool crib. An automated guided vehicle carries the tool magazine from the machine tool to the tool crib. Though this reduces tool changeover time, the additional cost of a replaceable tool magazine and the system of transporting it to the tool crib and back, makes it a more expensive proposition. However, it is possible to reduce the total number of tools in the system by making for a tool magazine with fewer tools. Though a number of systems, such as Yamazaki, Cincinnati Milacron, etc. were tried in the early eighties, this method is not being widely used in any of the newer systems.

Another alternative to the above system is, instead of replacing the entire tool magazine in one goes, breaking it into smaller segments called cassettes, so that each individual cassette is replenished at a time in place of the complete magazine. This would mean a small tool change time and comparatively straightforward way of replenishing the tools. The number of tools in the system would be more or less the same as in the first case.

There are a number of ways in which this method is adopted. In the Werner and Kolb system called Quick Tool Change (QTC), the cassette is in the form of a linear array capable of storing eight tools. A simple transfer machine which removes old tools with new tools by a comb cassette is incorporated. The chain tool magazine used in this case is divided into a variably overlapping storage and changing area as well as fixed areas for standard tools and worn tools. The machine tool automatically deposits the tools in the respective areas after their use in spindle. The movement into the respective areas of the magazine chain takes place parallel to the machining time. The tools, which are worn out are first transferred to the tool positions meant for transfer. Then the tool chain indexes to bring all the tools to the transfer position. The empty comb cassette would then transfer the tools from the chain. The cassette is withdrawn while a new cassette with fresh tools is brought to the tool change position. These tools then get transferred to the tool chain.

Another approach for a selective change of tools between the primary tool magazine and the secondary tool storage is to have a robot arm stationed between them. The robot arm can transfer tools as and when required. The secondary tool storage is exclusively meant for the single machine tool. This is the most generally adopted system in the case of a turning centre or turn-mill centre when modular tooling is employed. The modular tooling system may be the block tooling system of Sandvik, or Widaflex or Multiflex tooling of Widia, Karl Hertel's Flexible Tooling System, or Kennametal's KM Tooling. In this system, the tools to be transferred in the secondary tool storage are arranged as a linear matrix, from where the robot arm transfer it to the main tool turret. This type of tool magazine stores a large number of tools to provide for an uninterrupted production cycle. The same gantry robot also transfers the workpiece (with different grippers) kept on pallets.

Though this system suits a turning centre admirably, because of the low weight of the turning tools and parts, operating it would be difficult in the machining centres. In the case of turning centres, the tool change robot may also be used for work handling by adopting it as gantry with larger work envelope as used by Boehringer, Monforts, Traub and others. The gantry robot has the necessary capability to transfer the turning tools as well as the power tooling used in the turn- mill centres. This allows for the turning centre to effectively become a flexible turning cell. Also, the large expense involved in the making of the stand-alone material handling unit for each of the machine tools would make the system economically unsuitable. The tool transfer time in these systems is negligible since the transfer is affected when machining is being carried out.

One system which is currently emerging as the most promising and which has been adopted by practically all FMS manufacturers, is the single tool transfer method. Here each individual tool is transported to the tool magazine by means of a tool change robot travelling along a tool highway. This involves a single secondary tool storage consisting of all the tools for the complete system of machine tools. This would effectively reduce the duplication of expensive tooling, since the same tool can be used on more than one machine tool. It also helps in the simple upkeep of all the tools required for the system. The replenishment of the tools in the secondary tool store is generally manual.