CNC machines, garments, textiles

1. Sewn Products, Machinery & Equipments-II
CNC Fabric Cutting Machines
By :- Bittu Singh Presented to :- Mr. Ankur Makhija
Radhe Kumar
Shubham Singh

2. Computer Numerical Control
 Numerical control is a method of automatically operating a
manufacturing machine based on a code of letters, numbers, and
special characters.
 The numerical data required to produce a part is provided to a
machine in the form of a program, called part program or CNC
program.
 The program is translated into the appropriate electrical signals
for input to motors that run the machine.

3. Introduction
 For a CNC, machine control unit (MCU) decides cutting speed, feed, depth of cut, tool selection ,
coolant on /off and tool paths.
 The MCU issues commands in form of numeric data to motors that position slides and tool
accordingly.
 By integrating a computer processor, computer numerical control, or “CNC” as it is now known, allows
part machining programs to be edited and stored in the computer memory as well as permitting
quality control functions during the actual machining.
 All CNC machining begins with a part program, which is a sequential instruction or coded command
that directs the specific machine functions.
 The part program may be manually generated or, more commonly, generated by computer aided part
programming systems.

4. Program Input
Different ways of data input are :
 MDI : Manual Data Input
 PROGRAM PREPARATION WITH CAD /CAM
 PROGRAM DATA TRANSFER FROM PC TO CNC machine.
Cutting Speed
 Cutting speed varies from one fabric to the other.
 For densely woven fabrics (like denim), the speed required for cutting is more and vice versa.
 Knits can be cut at an average speed of 2,500 rpm while 14 oz. denim may require 7500 rpm to cut it.
 Some cutters also have a liquid silicon system with cooling device set up to at the top of the knife to
make sure that the heat is not generated and if it does the heat never reaches the top of the knife.
 Operators can easily adjust cut speed and knife speed according to the type of material being cut to
maximize throughput.
 Overall speed of cutting fabric is generally 5 to 12 m/min.

5. The Cutting Table
Bristle bed
 Nylon bristles present on the cutting table support fabric
layers. They are flexible enough to permit penetration and
movement of the knife blade which is supported only at
the top. These bristles allow the passage of air through the
table to create a vacuum, reducing the height of lay and
holding it in place.
 The bristle surface on the table allows knife blade to
penetrate surface without damage. Bristle cutting surface
automatically conveys material from spreading table
through cutter and after cutting is done, the conveyor
takes off cut panels into bundling area.

6. Vacuum System
 Vacuum system is required to hold the lay in place and reduce its height. So, it holds the layers while the
knife is cutting.
 There are three types of vacuum systems, depending upon the manufacturer:
1. TUB vacuum : Tub suction applies equal amount of suction overall the cutting area.
Integrated vacuum system holds materials securely in place for effective and accurate cutting.
2. LOCALIZED vacuum: Localized vacuum is used for creating suction only at areas surrounding the
blade and not the entire cutting area. Integrated "intelligent" zoned vacuum system holds down
the lay at cutting location. Vacuum exhaust stack recycles heated air.
3. PLY SENSING vacuum: This is a very efficient and power saving system of creating vacuum in the
cutting area. Amount of vacuum generated depends upon the number of fabric layers. Once
fabric plies are placed on the cutting table and vacuum generation is started, sensors detect
height of the lay and generate only the amount of vacuum sufficient for holding the layers. This
way energy consumption is reduced to a large amount in cases where length and of plies is
lesser than the cutting dimensions.

7. Role of re-sealer (polyethylene sheet)
 A sheet of airtight polyethylene covers
the top of the ply which assists the
creation of a vacuum & allows
significant compression of the lay. It is
done in order to prevent lateral air
flow from both the ends.
 The re-sealer is attached to the
cutting beam at a particular angle and
does not go up or down at the beam.

8. Role of perforated paper
Before transferring the fabric plies on the cutting table
, a sheet of perforated paper is spread. This paper is
laid so that the lay can be moved on the cutting table
without any distortion in the lay. This
paper is perforated to enable vacuum
creation on the cutting area for
compressing the lay. Perforated paper

9. Different aspects
 Role of laying marker
Marker is laid on the top ply to help in the process of bundling after cutting. Marker laid helps in the
identification of bundles of pieces by their size, style and other specific details.
 Order of cutting parts
If there is a small part between two large parts, then it must be cut prior to either of the big parts in order to prevent any
loss of vacuum created by cut lines and thus a support wall helps in getting better quality.
 Common line cutting
There are many common lines in the marker and CNC can’t see the whole marker as it only deals with one piece at a time.
So a gap of 1/8 th of an inch is added to avoid quality problems. But it leads to fabric wastage and time loss.

10. Characteristics
 CNC prevents on-grain cutting as there is a laser pointer which checks the direction of fabric lay.
The machine moves over the lay before cutting. The laser pointer checks the direction of fabric
selvedge and changes the blade orientation according to the grain .
 It is necessary to set the re- grinding frequency of cutting blade as the blade gets torn out day by
day so if we grind it by the same frequency it damages knife, therefore different grinding
frequencies are set for the blade.
 Long vertical knife strokes and automatic knife re-sharpening eliminate hanging threads ensuring
quality cut parts from top to bottom ply.
 A motorized drill behind the cutting head can provide drill holes as required.
 Maximum height of the lay to be cut is usually 7.5 cm when compressed.

11. Working Principle

12. Software Requirements
 Windows operating system
 Operator guide with plausibility control and fault diagnoses
 Automatic adaptation of inclined ply position to marker
 Elimination of common cut-lines
 Automatic chain up of markers
 Application for remote-service
G Code
 The "instructions" read by CNC machines are usually a human
readable format called G-Code. The machine is set up with a base
unit, like inch or mm, and a command of G01 X500 Y200 Z100 on a
metric mm setup tells the machine it needs to move.
 Example: 500 units on the X axis and 200 units on the Y axis and 100
on z axis.

13. CNC Programming
Programming consists of a series of instructions in form of letter codes.
Preparatory Codes:
 G codes-Initial machining setup and establishing operating conditions
 N codes-specify program line number to be executed by the MCU
 Axis Codes: X,Y,Z -Used to specify motion of the slide along X, Y, Z direction
 Feed and Speed Codes: F and S-Specify feed and spindle speed
 Miscellaneous codes –M codes For coolant control and other activities.

14. Hardware Requirements
 Reversible bristle conveyor
 X- and Y-axis driven by linear-modules
 Permanent-magnet-motor-drives for all axes
 Parameter driven adjustable vacuum
 Integrated sound absorber for exhaust
 Integrated cleaning of the bristles
 Sharpening device
 Automatic knife-frequency-dependent oil dosage
 Industrial PC on an actual performance level with flat screen
 Integrated high performance vacuum turbine, 15 kW
 Standard working widths: 1600/1800/2000/2200 mm

15. Basic CNC Principles
 All computer controlled machines are able to accurately and repeatedly control motion in various
directions. Each of these directions of motion is called an axis. Depending on the machine type there
are commonly two to five axes. Additionally, a CNC axis may be either a linear axis in which movement
is in a straight line, or a rotary axis with motion following a circular path.
 The most basic function of any CNC machine is automatic, precise, and consistent motion control -
the heart of CNC.
 Tool paths describes the route the cutting tool takes.
 Motion can be described as point to point, straight cutting or contouring.
 Speeds are the rate at which the tool operates e.g. rpm.
 Feeds are the rate at which the cutting tool and work piece move in relation to each other.
 Feeds and speeds are determined by cutting depth, material and quality of finish needed. e.g. harder
materials need slower feeds and speeds.
 Rouging cuts remove larger amounts of material than finishing cuts.

16. Work Positioning
 The method of accurate work positioning in relation to the cutting tool is called the “rectangular
coordinate system.” On the vertical mill, the horizontal base line is designated the “X” axis, while the
vertical base line is designated the “Y” axis. The “Z” axis is at a right angle, perpendicular to both the “X”
and “Y” axes.
 Increments for all base lines are specified in linear measurements, for most machines the smallest
increment is one ten-thousandth of an inch (.0001). If the machine is graduated in metric the smallest
increment is usually one thousandth of a millimeter (.001mm).
 The rectangular coordinate system allows the mathematical plotting of points in space. These points or
locations are called “coordinates.” The coordinates in turn relate to the tool center and dictate the “tool
path” through the work.

17. CNC Axis (x, y, and z)
 The z-axis is one of three axes for the CNC The z-axis allows the router to move in the up and
down direction. The CNC z-axis is very important to the CNC machines. Without this axis, depth
cannot be created.
 The function of the y-axis serves as a motor mount to move the z-axis in addition to the slide
mechanism.

18. Motion of knife

19. CNC FEED DRIVES
 Positioning accuracy, speeds of working motions, accelerations and smooth motions – all depend on the
feed drive system.
 Professional solutions require applying servo drives, and for less demanding applications, step motors are
sufficient.
 In the case of step motors all machine movements consist of a large number of single steps. Each step,
depending on the drive ratio and the amount of microsteps, is from 0005 to 0.1mm. Drives of this type have a
very simple structure, which results in a relatively low price. A certain disadvantage is the lack of the
measurement of position, and in certain difficult circumstances (overloading) the coordinates may be lost
(lost steps), which may cause damage to the processed work piece or the tool.
 Servo drives are devoid of such shortcomings. Their work consists in constant striving to achieve zero
deviation, i.e. the difference between the value set and the value measured. The head position is constantly
read by the incremental encoders, which can measure the position of the head with the accuracy coming up
to 0.001mm.. When the load increases, the engine increases the power to prevent arising the deviation of the
position, and in the case of exceeding a certain load, the system stops the machine and informs the operator
about the need for intervention.

20. Ease of operating
 Easily retrieve cutting setup files for quick retrieval to accelerate future cut jobs.
 Continuous, real-time, graphical display of operating parameters, vacuum level and cut speed provides
a comprehensive overview of the entire cutting process.
 User screen displays cut job, including the sequence of cut pieces, for verification; displays cutting
progress.
 Graphical user interface simplifies operator training and daily use

21. Advantages of CNC
 Flexibility of operation is improved, as is the ability to produce complex shapes with good dimensional
accuracy, repeatability, reduced scrap loss, and high production rates.
 Machine adjustments are easy to make with microcomputers.
 More operations can be performed with each setup, and less lead time for setup and machining is
required compared to conventional methods.
 Design changes are facilitated, and inventory is reduced.
 Programs can be prepared rapidly and can be recalled at any time utilizing microprocessors. Less
paperwork is involved.
 Faster prototype production is possible.
 Required operator skill is less than that for a qualified machinist, and the operator has more time to
attend to other tasks in the work area.

22. Advantages of CNC
 Volume of production is very high.
 Less paper work, faster prototype production, reduction in lead times.
 Improved quality and accuracy of manufactured parts
 Stabilized manufacturing costs.
 CNC machines can be updated by improving the software used to drive the machines.
 One operator can run two or more machine at a time hence reduces the labour cost.
 Shorter cycle time.
 Just in time manufacture.
 An automatic material handling.
 Lesser floor space.
 Increased operational safety.
 Machining of advanced materials.

23. Disadvantages of CNC
1)Higher investment cost :
The machine is expensive. High machine utilization is essential in order to get reasonable return on the
investment.
2)Higher maintenance cost :
The technology used in the CNC machine is to be more complex as
compare to the general equipment so it requires high maintenance cost.
3)Skilled CNC operator is required :
Part programming and CNC operation as well as maintenance requires the skilled operator to overcome
these problems.
4)Air conditioned place are required for installation of themachines.
5)Unsuitable for long run applications.
6)Training of part programmer is required.

24. References
 Tyler D. J. Carr & Latham’s Technology of Clothing Manufacture. Computer controlled cutting knives. Pg. Nos.
39-42. Fourth Edition. Blackwell Publishing.
 Smid P. CNC Programming Handbook. Industrial press Inc. Retrieved from : Google Books
 CNC Machine Overview. Retrieved from : Linux CNC
 Introduction of CNC Machines. Retrieved from : Scribd.com
 CNC. Retrieved from : Scribd.com
 CNC Machines. Retrieved from : TechnologyStudent.com
 Lectra Vector Series. Retrieved from : Lectra.com
 Gerber Cutter series. Retrieved from : Gerbertechnology.com
 Automatic Cutter Range. Retrieved from : Morgantecnica.com
 Automatic Fabric Cutting Machine. Retrieved from : Tukatech.com
 Automated Systems. Retrieved from : Eastmancuts.com
 Cutters. Retrieved from : Assystbullmer.co.uk
 High ply cutters. Retrieved from : Unionspecialcuttingsolutions.com
 Automatic cutters. Retrieved from : Europlotter.com