Contextualización del Programa Integral para la Superación Profesional del claustro en idioma inglés dentro de la estrategia de desarrollo de la

Tom Beard

This captive shop designs prototypes and fixtures right in CAM. A strong graphic visualization capability helps them develop the workpiece and machining process simultaneously.

Machine shops have been making things from sketchy design information for a long time. A customer describes what he wants, the machinist does his best to make it, and then the process of refinement begins. Once there's something solid to look at, they can get specific about what the real product should be. It's a time-consuming process, but at least there's little question as to physical appearance of the product.

Today, however, few companies can afford such a protracted development cycle. You still have to get it right, but the work has to get done in a fraction of the time.

This is one area where CAD technology has been particularly helpful. With CAD, designers more quickly and easily flush out their concepts, and get varying degrees of visual feedback as to what a mechanical part really looks like.

This way, the design can be scrutinized to a much greater degree before anything is machined, and then when the first prototype is produced, it's much closer to the desired result.

But CAD is really aimed at people who design all the time. CNC machinists think mostly about the manufacturing process, and what they want first is a tool to help them turn their process plan into a workable part program. But, increasingly, they also want the ability to visualize that machining process, much like the designer, to proceed with a higher degree of confidence that what happens on the machine tool is as close as possible to the intended result.

An interesting question is, when the machinist also occasionally functions as a developer of prototypes and a designer of tooling, how much CAD and how much CAM does he really need? One answer can be found in the machine shop of Nuclear Research Corp. (Dover, New Jersey), a manufacturer of radiation monitoring systems. This is one versatile shop. They do a limited range of CNC production machining. They make prototypes of those parts, as well as for parts that will eventually be cast. And they create a variety of fixtures both for their production machining and for the plant's printed circuit board assembly machines. To compress the development process of both fixtures and prototypes, shop manager Dennis Teske does his design work right in CAM. Besides being a more efficient way to go about these tasks, it provides the ability to clearly visualize both part and process, which

frequently are developed simultaneously. That's helping NRC develop new

designs faster and improving the efficiency of their own production work as well.

The Shop

Nuclear Research Corp. (NRC) designs and manufactures radiation detection instruments for both commercial and military use. Their equipment is just as likely to be found on the belt of an infantryman as the bench of a laboratory.

Reliability in harsh environments is critical, which puts a special emphasis on consistency and quality in their manufacturing operations, which meet MIL-Q-9858A and MIL-STD-2000 quality standards. The most critical components of their instruments are, of course, the radiation sensors themselves, along with the necessary circuitry. But virtually all the housing and internal

mounting components are made of metal, and they, too, must be made to exacting standards.

Though NRC has a line of standard products, much of their work is made to order. That creates a steady stream of work coming through the machine shop for prototypes, fixtures, and ultimately for low- to medium-volume production machining. In addition, the shop manufactures tooling for NRC's printed circuit board assembly operations. These are the fixtures that hold the boards as the various components are being inserted. Thus, machining processes can range from a fairly complicated quantity of one, to relatively simple machining of several thousand parts. All the milled parts are

produced on a Fadal vertical machining center. CNC turned parts are produced on a Miyano twin-spindle turn/mill center.

Actually, CNC is a relatively new addition to the shop. They historically produced tooling and prototypes on manual machines, and sent all the production work out. The Fadal was added two years ago (as was the turning center, later) primarily as a lower-cost means for production

machining, but it plays a very large role in the development work as well.

The other key resource is CAM; it is the Virtual Gibbs system (Gibbs and Associates, Moorpark, California), which is run on an Apple Macintosh

computer (the system also runs on IBM-compatible PCs) located right in the shop.

The variety of work creates an interesting mix of design and programming challenges for Mr. Teske. With prototypes, he's most concerned with quickly getting the geometry to a state where he and the original design engineer can agree on the details. With production work, he's focused on getting the most efficient process possible, which certainly requires the ability to quickly create and verify all tooling motions, but also involves the creative design of the workholders. And in all cases, he has to be able to make changes quickly and accurately.

A Better Picture

There are several reasons why this particular CAM system makes sense for this particular application, but clearly the most critical is its ability to

graphically render a part and/or process as it is being constructed. Quite literally, Mr. Teske gets a realistic picture on his computer screen that pays dividends in the time it takes to get the right results on the table of his machining center.

Looking at a prototyping process helps explain why. Though NRC's design engineers are an extremely competent group at dealing with demanding technical tasks, their primary concerns are not closely focused on the mechanical component parts of their instruments. They are expert at the application of radiation sensors, and at the design of the circuit boards that deliver the desired functionality of the product. They do care very much that these components are adequately protected, and they generate drawings and specifications to that end, but detailing the mechanical parts is

something they are happy to leave to the machine shop. And, historically, it was only after the first rough cut of a prototype that they got a really good feel for the physical characteristics of a design.

Now when Mr. Teske begins such a project, he first constructs the geometry in CAM. At this point, he is generally working in two dimensions at a time.

However, once he has the basic construction done, the system provides the ability to show that image as a realistically rendered solid model that can be rotated and viewed from any angle.

To Mr. Teske's machinist's mind, visualizing a part in three dimensions is second nature, so at this stage of the process, a 3D rendering may be helpful, but not critical, to his own work. However, it can be extremely valuable in discussion with an electrical engineer who has an entirely

different frame of reference. The rendering provides a model that he and the product design engineer can view together to ensure they have the same understanding as to the design intent and execution. It also provides the opportunity to discuss some elements of design optimization, for example, to address manufacturability issues that the 3D visualization of the part brings to light. Any problems that can be corrected at this early phase of the

prototyping process will save time down the road.

For parts they will machine in house, it may make sense to go ahead and create tool path code to more completely evaluate the manufacturability of the part. The CAM system provides a real-time solid model rendering of the machining process, which can be revealing as to its efficiency. This way, they can evaluate the design not just as a theoretical three-dimensional shape, but as a part created by a specific machining process. It's a tool that permits NRC to think about part and process at once, and still before

anything is committed to metal. If, through this simulation, Mr. Teske

detects areas where slight design modifications can help reduce cycle times

or the number of required tools, they can seize the opportunity for process optimization well before the design is finalized.

Such preprocess evaluations can be done with a part in its entirety, or a feature at a time, which is perhaps the defining strength of the Virtual Gibbs system. Graphic verification packages typically require that simulation come at the end of the programming process. Here, it is fully integrated so that a full simulation can be viewed of each machining process step as it is created.

Moreover, steps can easily be modified or resequenced, which is particularly important while the design is still in a fluid stage. Early on, Mr. Teske can run a range of "what-if" scenarios, or go ahead and create the entire program, yet still be able to go back to the program and make whatever necessary changes emerge.

Efficient Processes

This ability to work through part and process simultaneously is no less important to Mr. Teske's work in designing and building fixtures. Being a MIL-spec supplier, they have to think about building quality into their processes, and that applies just as much to the setup as to the machining process itself. Also, like any other business these days, NRC must contend with downward price pressure on their products, so they must find ways to lower processing costs. This, too, motivates the shop to make the most of their limited resources.

A key technique Mr. Teske employs is to machine multiple parts in a single setup. The idea is to use as much of the machine table as possible, reduce the load/unload time to the bare minimum, and design in a high degree of process consistency. Moreover, multipart machining reduces the

requirements for attendant manpower by combining the cycle times of even simple parts (with short cycle times) into an hour or more, therefore freeing the operator enough to execute additional tasks.

All of these considerations are built into the fixture, which Mr. Teske also designs in CAM. And here, too, he takes the broader view of thinking at once about the total process picture, rather than developing it in a linear chain, one step at a time. The idea is to visualize the entire setup in order to design the fixture and the machining process together.

The beginning premise is that as many parts as possible will be held on a base plate, the mounting dimensions of which are common to every production fixture in the shop. Mating reference pins are permanently

mounted on the table of the machine so that location of a fixture within the machine coordinate system is known at the outset, and is consistent among each fixture they use.

That established, Mr. Teske begins to think about which features can be machined in a given part orientation, and then how many parts can be crowded within the space defined by the baseplate to do that portion of the job. He will first decide what is required to hold a single part, and what space is required for tool clearance. Because he has the real part and baseplate geometry with which to work, and because they can be viewed from a 3D perspective, he is quite certain that what he is creating in CAM is workable within the physical constraints of the real machining environment.

Once the general fixture design is established, and the basic part program written, he runs a simulation of the complete machining process on a single part. Satisfied that it works, he then goes about flushing out the entire program

for all parts on the plate. Initially, that's a matter of establishing the location of each part. He might just step and repeat the entire machining process, part by part. However, it's more efficient to combine them all to minimize tool changes--so that, for example, the first operation is done to all parts on the pallet, then the second, and so on. This can be accomplished by

changing a single default in CAM, and further, the system can apply a degree of its own intelligence by automatically selecting the most efficient sequence. Mr. Teske may then elect to simulate the entire process, or just portions of it where he wants particular confirmation or suspects there may be additional opportunity to optimize the routine. And finally, the fixture is cut.

Critically important, this entire process has been developed within the context of the actual machine, tooling and workholder with which it will

occur. This is rather different than the typical programming scenario where a theoretical part is machined in space, and then it's left up to the operator to locate that process within the real-world coordinate system of the machine tool, and to contend with the often under-considered constraints of the workholder. At NRC, however, the whole process has been considered and verified in their CAM system well before the real setup begins.

Perhaps that's a subtle distinction to some people. But it can make a big difference in the time it takes to get new parts into production, and in the efficiency and quality of the production process itself.

COPYRIGHT 1994 Gardner Publications, Inc.

COPYRIGHT 2004 Gale Group

Impact of CAD surface modeling on CNC