lab 3 - cnc tooling

7/30/2019 Lab 3 - CNC Tooling

1/23

CNC Tooling

Lab 3:

Basics & Calculations


2/23

Vertical Mill Cutting Tools

Identify each cutting tool found on the millingmachine. (Attempt to be specific)

In teams of 3, compete to find the most information abouteach cutting tool One person in the text book One person on the internet One person in a machinery handbook

Limit the entire exercise to 30 minutes

The winning team will have the most individual pieces ofinformation about each cutting tool

Winning teams will have first access to the CNC Vertical Mill

Instructor: Stop Here for Students


3/23

Carbide Inserts

How would you characterize the carbide insert usedon the Vertical Mill?

In teams of 3, compete to find the most information aboutthat specific carbide insert One person in the text book One person on the internet One person in a machinery handbook

Limit the entire exercise to 15 minutes

The winning team will have the most individual pieces ofinformation about the carbide insert

Winning teams will be team captains for the team projects



4/23

Vertical Mill Spindle Speed

Feed rate for a cutting tool is dependent upon spindle speed.As 3 member teams, create lists to answer the following (limittime to 15 minutes): In manual mode, how is spindle speed controlled on the

VMC190xi? What options does the operator have for controlling/monitoring

spindle speed? What are the anticipated differences in torque and the resulting

stalling of the tool bit, with relation to driving horsepower of the

mill? What do you anticipate would happen if the mill is in CNC automaticmode and the tool bit stalls while cutting?



5/23

Answers

Spindle speed on the VMC190xi can not be accurately controlledby using the manual pushbuttons. Therefore, the only manualmethod of controlling spindle speed is through the Boxford

software. Optionally, an instrument that reads out in RPM can be mounted to

display spindle speed

As horsepower increases, the variation in spindle speed due tocutter loading decreases. Also, for machines with geared or beltdriven spindles, the slower spindle speeds at the same motor

speed will have more torque and less speed variation. When in CNC automatic mode and the tool bit stalls while cutting,

the table will further bind the tool into the work piece and maybreak the tool, damage the work piece, stall the x-y tablemovements,


6/23

Vertical Mill - Tapping

When tapping using a vertical mill, how is

torque on the tap limited to reducebreakage?



7/23

Answer:

Recommended Drill Bit size is chosen for tap A cutting fluid is specified for the material

Taps are discarded when worn Taps are matched to the materials machined Spiral fluted taps help minimize the torque while cutting threads

by keeping shavings from binding within the cutting edges A tap clutch accessory can be purchased for about $500 which

can be programmed to slip at specific torques

A reversing motion is needed by some taps to clear metalshavings to prevent binding

Some milling machines have torque sensors that allowfeedback to reverse the spindle when a preset torque isexceeded


8/23

Calculating Spindle Speed

Each material has recommended cutting

speeds listed in sfpm.

Sfpm = 3.14 x tool diameter x RPM12

Solve for RPM


9/23


If a material calls for an optimal cutting rate

of 250 feet per minute, what should thespindle speed be set at?

Assume end mill

Aluminum stock



10/23


RPM = SFPM x 12

Tool Diameter 3.14 RPM = 250 x 4 x 12

1 3.14

RPM = 3822 or about 3800 rpm


11/23


Using Appendix C, what size of end mill and

spindle speed should be used when millingaluminum?

As a 3 member team, determine the appropriaterelationships

Limit this exercise to not more than 15 minutes



12/23


Aluminum sfpm = 250 when using HSS Sfpm = (tool diameter) x RPM x 3.14 / 12

Solving for variables on one side and constants on the other RPM x tool diameter = SFPM x 12 / 3.14

Therefore, for any tool diameter there is a unique spindlespeed, but there is no ideal tool diameter and speed

combination tool diameter is restricted by available power, clamping of the

material, the smallest radius feature of a machined object,and other criteria


13/23

Calculating Tap Feed Rate

Given the requirement to tap a -20prepared hole in a aluminum plate;

what 2 pieces of information are necessaryto manually control the tap operation alongthe z-axis?

How many seconds will it take to tap each holeusing spindle speed calculations?


14/23

Hint

Aluminum sfpm = 250

1/4x20 tap ~1/4 diameter cutting surface RPM = 250 x 4 x 12 = 4000 rpm

1 3.14

20 threads per inch or 10 threads per

1 revolution per thread



15/23

Answer

10 revolutions x min x 60 sec = 0.15 sec4000 rev 1 min

Therefore, such operations can only be performedusing CNC equipment Slower manual operations can be performed at a cost of

labor

Always check the tool manufacturersrecommendations for determining best spindlespeeds, appropriate cutting fluids,


16/23

Calculating Feed Rates

Associated with Feed Rates are the actual

table positions in the X and Y axis Using full size manual vertical mills, how are the

actual positions of the X and Y axis

controlled/measured?

Go to the next page for a picture of a full sizemanual vertical mill


17/23

Full Size Vertical Mill


18/23

Manual Feed Rates

What are the options for manual feed ratecontrol/monitor of the x-y axis on theVMC190xi? Setup the Boxford Software to display the manual

control of x-y axis feed rates Each team should be splitting the tasks

There are 4 computers with identical software, hooked todifferent types of machines

The Boxford manuals can be accessed on all of the labcomputers, and also from the NSF sponsored Wikiwebsite


19/23

Team Problems

Youve had several opportunities thus far to operate

as a TEAM List your insights as to why you believe the team suffers in

certain areas

Separately list what benefits you achieved by working as ateam

As a class, create a comprehensive list of rules foroperating as a team

Limit this exercise to not more than 20 minutes


20/23

Evolved List of Team Rules

Every semester the class has been asked to do this exercise,and the following is a compiled list of rules that students havecited that are believed to contribute to team productivity use the Result Management tool cited earlier if there is a conflict


21/23

CNC machining from CAD Drawings

Capturing the specific features of a design in

a binary file provides the opportunity tomachine parts in an automated mode

Remove the tooling from the VMC190xi andput the mill in the Home Position

See Lab 2


22/23

Selecting a sample CAD drawing

Video for CAM implementation of a sample

CAD drawing goes here


23/23

Run the CAM software without tooling

For the remainder of the lab, every student should remove all tooling and work pieces from the 4 CNC

machines Start each CNC machine

Put each machine manually in the Home Position

then mock machine a sample CAD file Be ready to hit the Emergency Stop Button to prevent a

collision between the spindle, vise, x-y table, chuck, wallsof the enclosure,

If time permits, introduce precision orientation ofthe bench vise

lab 3 - cnc tooling

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