CNC Machining Fundamentals

CNC Machining Fundamentals
Applied Fundamentals

FOR COMPANIES WITH A MANDATE TO CONTROL MANUFACTURING COSTS AND CAPITAL EXPENDITURES.

MACHINE TOOLS RUNNING EFFICIENTLY AND PRODUCING GOOD PARTS.
QUANTIFIABLE RESULTS WITH CHECKS AND BALANCES.
No smoke and mirrors, spin or red herrings.

Manufacturing Alliance Associates, Inc.

720 Maple Street, East Aurora, New York 14052-1012 716-652-4510

Machining Cost - do the math - (it's only industrial engineering fundamentals and simple algebra).

Financial equations for analyzing machining performance.

Standard hours = base time + allowances

Actual hours = standard hours / efficiency

Efficiency = standard hours / actual hours

Paid hours = actual hours + delays

Yield = standard hours / paid hours

Paid hours = standard hours / yield

Utilization = actual hours / paid hours

Machining Setup Reduction - (simply make the observations in your environment, you'll be surprised).

Fundamental direct and indirect labor tasks performed in cnc machining operations.

A simple definition of setup time is the total base tasks plus allowance factors for the time it takes to go from the last piece in the present work order to the first good piece in the next work order. Setup time can range from 5% to 95% of the time applied to a work order. The percentage increases as the lot size decreases, significantly effects the unit cost of each part in a work.

To go from one work order to the next on a CNC machine tool the following tasks generally occurs:

tearing down tool holders
assembling tool holders
locating and securing work holding devices
measuring program zero
entering offsets for program zero and for tool diameters and lengths
loading the program into the machine control unit
verifying the program
inspecting the first piece
and, optimizing the program if it is the first release of a work order

The machine is down while the above tasks are performed. These can be defined as on-line tasks.

Tasks performed while the machine is producing good parts can be defined as off-line tasks. These tasks include programming and searching for tools, gages and fixtures for the next work order while the machine is running. The smaller the lot size, the harder it is to perform off-line tasks, and the fewer the people available in the overhead structure, the more tasks are performed on-line.

Based on the definition of these tasks, setup time can be defined as the total of the on-line tasks. Three methods of reducing setup time are:

eliminate on-line tasks
perform on-line tasks off-line
facilitate on-line tasks

Before starting a CNC setup time reduction program, first dedicate time, effort and people to evaluate and document your current setup procedures. Next, weigh the cost of implementing any of the following recommendations to remove wasted time:

1. Apply CNC technology on-line.

Use a spindle probe to correctly and automatically load work coordinate offsets for program zero measurements, eliminating edge finders and dial indicators.
Use a tool probe to correctly and automatically load tool length offsets.
Add more memory to the machine control unit (MCU) to leave programs in the control.
Background edit while the machine is running.
Prove out programs using the block delete function.

2. Move on-line tasks off-line.

Verify NC programs on a PC and then download the programs to the MCU instead of using an expensive CNC machine tool as a plotter.

3. Facilitate on-line tasks.

Organize tools, fixtures and gages.
Build tool assemblies during production.
Dedicate preset tooling for high usage tool.
Run orders in a logical order.

Machining Statistical Process Control

Fundamental capability measurement of the machining operation process.

Capability is a measure of whether or not the parts which the process is currently producing are within the tolerance limits.
Capability equals print tolerance 6 standard deviations (actual distribution).
Capability is a measure of whether or not a process is capable of producing parts to print.
Capability should always be > 1.0.
Cpk should always be > 1.0.

Machining Parameters

Fundamental formulas to derive the machining parameters based on the work piece material type and condition.

Machining Hourly Rate

Financial equations for analyzing machining performance.

Fundamental direct and indirect labor tasks performed in cnc machining operations.

Fundamental capability measurement of the machining operation process.

Fundamental formulas to derive the machining parameters based on the work piece material type and condition.

Appling today's technology without Model-T Ford accounting practices.