Feature-Based Machining (fbm)

FBM uses only solid models for part geometry. With a single operation, FBM analyzes a the model, detects all machining definition features in a specified plane, and automatically generates all of the 2-D milling toolpaths necessary to completely machine the selected features (Fig. 9.3).

For complex nested pockets, Mastercam X creates a separate zone for each depth and creates the boundaries required to machine it. In the following example, six zones were created and machined separately (Fig. 9.4).

Figure 9.3 – Programming these nested pockets would be a snap with FBM.

Figure 9.4 – Mastercam X creates zones to be completed in stages.

Rest Milling

Based on a solid model, rest milling compares roughing results to the solid model in order to identify uncut metal, then creates a dynamic toolpath that removes the “rest” of the uncut material (Fig. 9.5). Efficient for the programmer and the machine cycle time, dynamic rest milling solves the issue.

Figure 9.5 – Rest mill creates an efficient follow-up toolpath.

Optimized Roughing (Opti-Mill). In standard roughing, we tend to make several down passes in stages. Mastercam’s 3D, OptiCore, OptiArea, and OptiRest toolpaths support cutters capable of machining very large depths of cut. It uses a fast, aggressive, intelligent roughing algorithm based on 2-D high-speed dynamic milling motion.

Peel Mill 2-D. High-speed peel mill toolpaths allow for efficient constant climb milling between two selected contours or along a single contour. It uses a trochoidal motion with accelerated back feed moves when the tool is not engaged in material. Peel mill can machine more than one contour by selecting them together.

References: Gen [1-3].

Assessing questions:

1. What is the features of the chip thinning?

2. How to achieve less radial engagement?

3. The purpose of using Feature-Based Machining?

4. When it is used the rest milling?

5. Advantages of the optimized roughing?

Lecture 10. Operating systems, basic software for controlling the CNC machines; the overall structure of software packages for CNC systems, programming methods

E-stop button. The big red button that depowers all machine functions. May require several actions to restart after touching this button.

Initialize (initialization). A process through which some CNC machines are brought up to full operational readiness. May be semiautomatic or may need intervention.

Lockout key switch. A multilevel switch that, with the key removed, allows or disallows certain control functions and authorities.

Midcycle stop (midauto halt). A way to quickly stop a program run without losing physical position or program data.

Overt (action). A deliberate and often difficult move to ensure it isn’t done by accident.

RIS (reduced instruction set) controller. Reduced instruction set controls using icons and double function buttons to create a super-compact control pad.

Soft limits. A switch that halts or slows rapid axis motion, before reaching hard limit switches, to prevent accidental overtravel of axes into full mechanical limits.

PC-Based Controls

There is a controller based solely on a standard PC. Any fast processor and hard drive can store and read a program, then send a signal to the axis drive relays. Many machine manufacturers offer PC-based systems as an option.

Familiar Operating Systems Using everyday operating systems such as Windows® or Unix®, PC-based CNC controls offer:

• Huge hard drive capacities to hold long programs.

• Standard hard drive and computer components that bring interchangeability and easy repair when necessary.

• CAD/CAM that can be performed at the CNC machine if the software is loaded.

• Part inventory using barcode scans.

• General shop communications such as e-mail, work order, or engineering drawing downloads.

• The ability to perform statistical process control charting and all sorts of other tasks right at the CNC machine.

Most PC-based controls include an operator pendant to assist with setup and program-run functions.

Tool Path Graphics Screens

1. Program Monitoring

This process tracks the position of a cutting tool using a picture of the progress. When coolant, chips, and safety shields obscure the machining, this is one way of tracking progress.

2. Program Dry Run

The first test of a program can be made on the video screen with all axes locked out – using the slide hold or axis lock switches. The graphics will provide a rough picture of the program path with no material being machined.

3. Graphic Programming

An option on some advanced controls, the program is developed by drawing elements on the screen similar to CAD drafting.

References: Gen [1-3].

Assessing questions:

1. What is E-stop button?

2. How can be operate the process of initialization?

3. How can be controlled CNC machines based on PC?

4. What is the tool path graphics screens?

5. Graphic programming.

Lecture 11. G-codes part programming

The programming language of the mill is known as G-code. A G-code program is composed of one or more lines of code. Each line (called a block) may include commands to the machining system to do several different things. Blocks may be collected in a file to make a program.

A typical block consists of an optional line number at the beginning followed by one or more words. A word consists of a letter followed by a number (or strictly speaking, something that evaluates to a number). A word may either give a command or provide an argument to a command. For example, G01 X3 is a valid line of code with two words. G01 is a command meaning move in a straight line at the programmed feed rate, and X3 provides an argument value (the value of X should be 3 at the end of the move). Most commands start with either G (general) or M (miscellaneous). The words for these commands are called G-codes and M-codes.

The language has two commands (M02 or M30), execution of either of which ends a program. A program may end before the end of a file. Lines of a file that occur after the end of a program are not to be executed in the normal flow, so generally they’re parts of subroutines.

A block (or equivalently line) of code is a section of programming language elements that are grouped together into a single statement. A program consists of one or more blocks, each separated by a line break. Blocks in a program are executed sequentially from top to bottom or until an end command (M02 or M30) is encountered.

A real value may be an explicit number (such as 341 or -0.8807), a parameter value, an expression or a unary operation value. Definitions of these follow in the Word Initial Letters table.

Numbers are a subset of real values. Processing a real value to come up with a number is called evaluating. An explicit number evaluates to itself.

The following rules are used for explicit numbers. In these rules a digit is a single character between 0 and 9.

• A number consists of the following, in order: (1) an optional plus or minus sign, followed by (2) zero to many digits, followed, possibly, by (3) one decimal point, followed by (4) zero to many digits.

• There must be at least one digit somewhere in the number.

• There are two kinds of numbers: integers and decimals. An integer does not have a decimal point in it; a decimal does.

• Numbers may have any number of digits, subject to line length limitations.

• A non-zero number with no sign as the first character is assumed to be positive.

Initial zeros (before the decimal point and the first non-zero digit) and trailing zeros (after the decimal point and the last non-zero digit) are allowed but not required. A number written with initial or trailing zeros has the same value when it is read as if the extra zeros were not there.

Numbers used for specific purposes by the operating system are often restricted to some finite set of values or some to some range of values. In many uses, decimal numbers must be close enough to an integer to be accepted as input. A decimal number which is supposed to be close to an integer is considered close enough if it is within 0.0001 of an integer.