Wireframe and solids

Compared to hand-compiled programs, CAM programming is faster, eliminates human math errors, and turns hours into minutes. CAM makes possible the programming of shapes and toolpaths that can’t be achieved by any other means. They could never be handwritten, no matter how capable the programmer might be. It’s called graphic interface (GI) programming.

A GI program can be based on three different kinds of part picture definitions:

1. A wireframe drawing (still effective for 2-D work)

2. Surfaces

3. But evermore the template is a solid model for good reason (Fig. 6.1a and Fig. 6.1b)

Solids bring more automation to the process because they are the part, with complete feature and dimensional information built in. They can even have material characteristics. A solid provides information the CAM system can use with less intervention from the programmer.

Figure 6.1a and 6.1b – Part geometry can be a wireframe, but solids work better -especially when part shape is complex.

Pockets are internal areas to be removed. When working with solid models, they can be defined by selecting a floor face or its bottom edges or sometimes by the surrounding walls. If using wireframe geometry, pockets are defined by the rim lines.

Contour (Profile or Peripheral Milling). This operation uses the cutter’s side teeth to mill the outside wall of the part, using either solids or wireframe lines. Now here is a huge difference: when selecting a contour from a wireframe, the user must tell the program to which side of the definition line the cutter must machine. Without indicating to which side the machining is to occur, CAM system cannot determine which side is metal and which is not - lines are all that exist, no material. With a solid this issue goes away - there is metal and not-metal (air). If the wireframe is a flat drawing without depth, that must also be provided by the programmer—but not when using a solid. Contour depth is on the part.

References: Gen [1-3].

Assessing questions:

1. What is the tool for boring?

2. What kind of drilling related operations do you know?

3. Computer-assisted machining.

4. What the difference between wireframe and solids?

5. What is pockets?

Lecture 7. Part program verification. Operating a CNC machine. CNC planning. Controller alarms. Operator actions. Monitoring and adjusting.

Milling is a machining operation in which a workpart is fed past a rotating cylindrical tool with multiple cutting edges. The axis of rotation of the cutting tool is perpendicular to the direction of feed. The cutting tool in milling is called a milling cutter and the cutting edges are called teeth. The geometric form created by milling is a plane surface.

There are two basic types of milling operations, shown in Figure 7.1: (a) peripheral milling and (b) face milling.

Figure 7.1 Two basic types of milling operations: (a) peripheral or plain millingand (b) face milling.

Peripheral milling. In peripheral milling, also called plain milling, the axis of the tool is parallel to the surface being machined, and the operation is performed by cutting edges on the outside periphery of the cutter. Several types of peripheral milling are shown in Figure 7.2: (a) slab milling, the basic form of peripheral milling in which the cutter width extends beyond the workpiece on both sides; (b) slotting, also called slot milling, in which the width of the cutter is less than the workpiece width, creating a slot in the work—when the cutter is very thin, this operation can be used to mill narrow slots or cut a workpart in two, called saw milling; (c) side milling, in which the cutter machines the side of the workpiece; (d) straddle milling, the same as side milling, only cutting takes place on both sides of the work; and form milling, in which the milling teeth have a special profile that determines the shape of the slot that is cut in the work.

In peripheral milling, the direction of cutter rotation distinguishes two forms of milling: up milling and down milling, illustrated in Figure 7.3. In up milling, also called conventional milling, the direction of motion of the cutter teeth is opposite the feed direction when the teeth cut into the work. It is milling ‘‘against the feed.’’ In down milling, also called climb milling, the direction of cutter motion is the same as the feed direction when the teeth cut the work. It is milling ‘‘with the feed.’’

Figure 7.2 – Peripheral milling: (a) slabmilling, (b) slotting, (c) side milling, (d) straddle milling, and (e) form milling.

Figure 7.3 - Two forms of peripheral milling operation with a 20-teeth cutter: (a) up milling, and (b) down milling.

Face milling. In face milling, the axis of the cutter is perpendicular to the surface being milled, andmachining is performed by cutting edges on both the end and outside periphery ofthe cutter. As in peripheral milling, various forms of face milling exist, several of which are shown in Figure 7.4: (a) conventional face milling, in which the diameter of the cutter is greater than the workpart width, so the cutter overhangs the work on both sides; (b) partial face milling, where the cutter overhangs the work on only one side; (c) end milling, in which the cutter diameter is less than the work width, so a slot is cut into the part; (d) profile milling, a form of end milling in which the outside periphery of a flat part is cut; (e) pocket milling, another form of end milling used to mill shallow pockets into flat parts; and (f) surface contouring, in which a ball-nose cutter (rather than square-end cutter) is fed back and forth across the work along a curvilinear path at close intervals to create a three dimensional surface form.

(a) conventional face milling, (b) partial face milling, (c) end milling, (d) profile milling, (e) pocket milling, and (f) surface contouring.

Figure 7.4 – Face milling.