CNC Machine Tools | Automatic Tool Changers | Multi Pallet Machines

TOOLING FOR CNC MACHINES

The special design features of CNC machines have resulted in use of higher cutting speeds and feeds, leading to considerable saving in the cycle time. To fully exploit the higher metal removal rates of the CNC machines, the tooling used should be able to withstand the higher cutting forces in the process and help to reduce the down time to a minimum possible. The tooling used on CNC machines should be:

(a) Rigid to withstand high metal removal rates

(b) Capable of being pre-set and re-set in the shortest possible time to keep the down time to minimum.

Accurate enough to produce repetitive accuracy on the job. In conventional machines, the cutting tool cuts metal for about 25% of the total machining time whereas the CNC machine tools are expected to cut metal for 70 to 80% of the time. Since CNC machines are very costly, the down time on these machines has to be reduced to a minimum. The tooling for CNC machine tools includes the cutting tools, and tool and work holding device.

01-CNC machine tools - Work holding devices

Automatic Tool Changers

The CNC machines are intended to perform a number of operations in a single setting of the workpiece. To decrease the down-time in change-over from one operation then to the next, the CNC machines are furnished with automatic tool change facility. The tool is automatically selected and changed based on the tool control function (T-word) in the part program.

Turning centres are available with the tool turret containing 6 to 12 tools. As the tool change command is acknowledged by the control system, the tool turret moves to a fixed tool change position and the required tool comes to the cutting position.

01- automatic tool changer in cnc machines - ATC - turning centers

On the machining centres, automatic tool changers (ATC) are provided to reduce the idle time between changes over from one operation to another. The ATC consists of a tool magazine for storing the tools and a tool change unit for transferring the tool from top magazine to spindle. The tool previously fixed on the spindle is removed and replaced in the tool magazine. The initial position of various tools is fed to the control system, which then keeps updating the data regarding tool number fitted in the particular pocket in the tool magazine. Tool magazines with up to 60 tools are quite common in India. The tool change cycle consists of two parts:

(i) Tool Selection Cycle

The tool for successive operation is selected during the previous machining operation. The selected tool comes to the tool change position, whenever the tool selection command is received by the system.

(ii) Tool Transfer Cycle

In this part of the tool change cycle, the tool which is lying selected in the magazine, is transferred to the spindle and the tool which is in the spindle is transferred to the magazine. Before the tool transfer takes place, the spindle is turned off and moves to the tool change position, so that the tools will not hit the workpiece.

Multi-pallet Machines

To further reduce the non-productive time, the CNC machines are provided with automatic pallet change systems. Twin-pallet CNC machines are very common but machines with up to 5 pallets are also being used. The multi-pallet system enables the operator to load the workpiece on one pallet while machining of workpiece on second pallet is going on. This helps in rapid change of workpiece, thereby reducing the idle time of the machine.

01 - multi pallet machines in cnc - automatic pallet change system

Unconventional Machining Process | Non Traditional Manufacturing Process | Modern Machining Methods

Modern Machining Processes:

DENZA wird in einem deutsch-chinesischen Gemeinschaftsunternehmen von Daimler und BYD in Shenzhen gefertigt. / DENZA is manufactured by a Sino-German joint venture of Daimler and BYD in Shenzhen.

In the past two decades some ultra hard and difficult to process of metals and alloys are not easy to manufacture, but continuous research on this field will produce rapid growth in this modern machining technology. The concept of material removal by Conventional edged tool machining is uneconomical for such harder and difficult to manufacturing materials and the degree of accuracy and surface finish attainable is poor. These edged tools machining involving plastic deformation and formation of chips has been known to man for several hundred years. The higher strength level would have a disastrous effect on the total machining bill if there was no corresponding improvement in machining technology. In view of the significance of this problem, Merchant (1960) highlighted the need for the development of newer concepts in metal machining; By adopting a integrated plan and utilizing the results of basic and applied research, it has now become possible to process some of the materials which were formerly considered to be unmachinable under normal conditions. Some of these methods have been commercially exploited while others are still in their experimental stages. The so developed newer machining processes are often called as “modern machining processes” or “unconventional machining processes”. The name unconventional implies that conventional tools are not engaged for metal cutting; rather energy is utilized in its direct form.

Modern machining processes are classified according to the type of fundamental machining energy employed, such as mechanical, electrochemical, chemical or thermoelectric.

Classification of Unconventional Machining Processes

Type of Energy

Metal Removal Mechanisms involved

Transfer Media

Energy Sources

Modern Manufacturing Process

Mechanical

Erosion

High velocity particles

Pneumatic/

hydraulic

pressure

Abrasive Jet Machining (AJM), Ultra Sonic Machining (USM), Water Jet Machining (WJM)

Shear

Physical contact

Cutting tool

Conventional machining

Electrochemical

Ion displacement

Electrolyte

High current

Electro Chemical Machining (ECM), Electro Chemical Grinding (ECG)

Chemical

Ablative relation

Reactive environment

Corrosive agent

Chemical Machining (CHM)

Thermoelectric

Fusion

Hot gases Electrons

Ionized material High voltage

Ion Beam Machining (IBM), Plasma Arc Machining (PAM), Electro Discharge Machining (EDM)

Vapourization

Radiation

Amplified light

Laser Beam Machining (LBM)

 

Ion stream

Ionized material

Plasma Arc Machining (PAM)

PROCESS SELECTION

To make effective utilization of advanced machining methods, it is important to know the precise character of the machining issue. It is to be comprehended that:

(i) these methods cannot replace the conventional machining processes and

(ii) a particular machining method found suitable under the given conditions may not be equally efficient under different conditions.

A careful assortment of the procedure for a given machining issue is fundamental.

 

Before selecting the process to be employed, the following aspects must be studied:

(i) Physical parameters.

(ii) Properties of the work material and the shape to be machined.

(iii) Process capability.

(iv) Economic considerations.

When comparing the physical parameters of modern machining processes, it may be noticed that both EDM and USM require approximately the same power, whereas ECM consumes roughly forty times more power than EDM. ECM consumes much greater power, it is an excellent method for drilling long slender holes with length/dia ratio > 20. It can be seen that for the machining of electrically non-conducting materials, both ECM and EDM are unsuitable, whereas the mechanical methods can achieve the desired results.