Metal Cutting 7

Question 1

What are machining centres?

Answer 1

Machining centres eliminate the need for

significant amount of part transferring during complex part manufacture

Question 2

How do machining centres work?

Answer 2

They can perform many cutting operations by using multiple spindles, large pre-set tool storage, automatic tool and part changing systems, and computer controlled motions.

Question 3

Pros of machining centres

Answer 3

Cost per part can be very low. Provides high dimensional accuracy and less human intervention. Suitable for low and medium volume production of parts. Suitable for production lines with variety of parts.

Question 4

Cons of machining centre

Answer 4

Initial cost can be very high

Question 5

What is meant by work envolope?

Answer 5

The maximum cutting dimensional capability of the machine

Question 6

How are machining and turning centres set up?

Answer 6

Designs in types of horizontal, vertical or combination of spindles

Question 7

What is a Universal machining centre?

Answer 7

equipped with several spindles and tool holders. Parts
typically locate on a rotary tables that provides extra axes to the machine. Pallets are used to automatically position parts.

Question 8

What are vertical spindles used for?

Answer 8

Suitable for flat surface and deep cavities because the cutting forces are transferred to the machine bed, thus better stiffness. Cheaper than horizontal spindles.

Question 9

What are horizontal spindles used for?

Answer 9

suitable for larger parts locating on
a pallet with multiple cutting processes on
different part surfaces.

Question 10

What is a gantry machining centre?

Answer 10

designed for machining large and heavy parts. Work piece is typically fixed on the bed and the cutting
head moves in several directions. Multiple cutting heads may be attached to the gantry and they could be controlled independently from each other.

Question 11

What is robotic machining used for?

Answer 11

a very flexible cutting operations such as drilling and milling for parts that are not accessible (due to safety or size). The accuracy of the advanced robotic cutters may reach to standard machining centres, but most robots lack stiffness required for machining.

Question 12

What is meant by a half axis?

Answer 12

refers to the 4th axis moving independent from other axes and not controlled automatically while cutting is in
progress.

Question 13

What are CNC machining centres?

Answer 13

A CNC machining centre has multiple horizontal and vertical spindles and several tool turrets. The motion of the tools/spindles are relative to the part movement and controlled by computer.

Question 14

What are pallets?

Answer 14

Pallets transfer parts to the spindle and locate in correct position. Pallets usually equipped with part holding fixtures, design generically for a family of parts or specifically for a certain workpiece. Multiple parts could be held by the fixture.

Question 15

How are tools changed?

Answer 15

An automatic tool changer is designed to exchange tool between tool storage drum or Tool Magazine
and the machine spindle.

Question 16

What is an open loop system?

Answer 16

the motion is not verified and the dimensional accuracy

depends on the accuracy of the machine components and the cutting forces.

Question 17

What is a closed loop system?

Answer 17

In the closed loop system a continuous feed back

verifies the exact movement of the work table as programmed.

Question 18

What is a recirculation ball screw?

Answer 18

used in the table lead screw to transfer accurate movement to the table, eliminating the backlashes and oscillating movement caused by some servomotors.

Question 19

What is a touch probe?

Answer 19

used in machining centres for determining workpiece and tool positions and surfaces relative to the machine table or column. Touch probes are used to determine (a) the X-Y (horizontal) and Z (height) of a horizontal surface, (b) the position of the surface of a cutter