Week 5:- Rest Unit & Clamp Unit Design Challenge

DESIGN OF POWER CLAMP UNIT

OBJECTIVE:

To design 3 different types of power clamp unit with different riser,blade,block and clamp arm & to design different types of rest unit for the given car panel.

SOFTWARE USED:

CATIA V5

CLAMP UNIT:

A clamp unit is a unit designed to hold/clamp the car panel with NC blocks/mylars/rest by using a pneumatic cylinder.

Clamp arm,finger,rest/backup,L-block,shims,riser,pneumatic cylinder are the typical parts of the clamp unit.

clamping force should be considered while designing clamp unit.

REST UNIT:

A rest unit is used to support the car panel,also it resists the clamping force of the finger with the help of rest mylars & thus clamp the car panel.

Rest unit consists of rest mylars , shim packs,riser.

Clamping force should be considerd while design rest unit.

Mostly to avoid extra part ,to reduce the weight & to reduce the cost of the fixture the rest unit is combined with the clamp unit.

Below figure shows the combination of clamp and rest unit which is designed in this project by considering the basic principles of clamp and rest unit.

TYPES OF CLAMP & REST UNIT:

• Power clamp unit.
• swivel cylinder clamp unit.

In this project i used power clamp unit to design.

PURPOSE OF CLAMP & REST UNIT:

The purpose of clamping tools is to securely hold the workpice in position without obstructing the productio process.High clamping force combined with compact dimensions are therefore the most important requirements for a clamping tool.For this reason,clamps are equiped with mechanical transmison gear units.

CLAMPING:

The process of holding the position of the workpice in the jig or fixture is called clamping.The priary device used for holding a workpiece are clamps/clamp unit.

RESTING:

The car panel rests on th rest unit,Also it resists the clamping force for the finger & thus clamp the car panel.

CLAMP ARM OPEN POSITION:

In this project , clamp arm open position and closed position also done.Here are some images of clam arm open position and closed position,

CLAMP ARM OPEN POSITION

CLAMP ARM CLOSED POSITION

FORCES ACTING IN CLAMP & REST UNIT:

To design a clamp unit we have considered some forces which acts in clamp unit for clamping purpose.The forces acts in clam unit are,

clamping force

Holding force.

clamping force is not same as holding force

CLAMPING FORCE:

Clamping force signifies the force applied to the worpiece by the drive mechanism via the clamp arm during gripping or clamping operations.

CLAMPING FORCE (Fs) = 48*S^3 = FORCE IN NEWTON.

HOLDING FORCE:

Holding force, on the other hand , denotes the maximum force ,after knocking the knee-lever( over center position),That can be applied by the workpiece on the griper/clamp arm without destroying the mechanism.

Therefore,particular attention must be paid to the maximum force when,for example during the production process(welding) there is a posibility of the destrotion of the component or if the clamp arm is used as a fixed stop.

If the holding force specified inthe technical details is exceeded, this will inevitably result in destruction of the mechanism,the clamp arm or the bearing position.

PLP LOCATION & CLAMP PLAN:

PLP(principle locating points):

Principle locating points which are used for the accurate location of the panels subassemblies to maintain the geomatry of the assembly.

There are lots of holes on the panel which are not accurate due to stamping operations.so plp are defined in the drawings.

The plp holes very much precise.

CLAMP PLAN:

Clamp plan provides the information of location of pins,rest units,clamp unit,dumps ,etc.

It is the important input from the customer.The clamp plan /position should not be changed without the knowledge of customers.

It gives the detail of the exact position of the clamping units by mentioning a coordinates in the particular position.

FORMULA & CALCULATION:

1. Validate or selecting a power clamp cylinder.
2. Clamping force acts at the end of each mylars.
3. Holding force.

• validate or selecting a power clamp cylinder:

I have designed selection of clamps on the basis of outreach & sheet thickness.

1. How to choose sheet thickness?

1. The thickness of panel is said to be considered as 1mm for this project.

ii.How to find out outreach of clamp arm?

By measuring the distance between pivot center of cylinder and center of clamping mylars we can get the outreach of clamp arm .

below given detials are the outreach of the clamp arm taken from the respected clamp unit used in this project.

1.P001_Z001_ST11_04_00_POWER_CLAMP_UNIT-1 -Outreach of the clamp arm is 120

2.P001_Z001_ST11_05_00_POWER_CLAMP_UNIT-2 -Outreach of the clamp arm is 120

3.P001_Z001_ST11_06_00_POWER_CLAMP_UNIT-2 -Outreach of the clamp arm is 120

After choosing the sheet thicknes and outreach of the arm ,now we can refer the graph shown below for selecting a suitable power clamp cylinder as per our requirement.

By relating the sheet thickness & outreach from the above graph,we can find the bore capacity of clamp cylinders.Based on the bore capacity the cylinders will be selected for the clamp unit.

MATERIALS USED:

In genral, materials used for mylars,clamp arm,shims,shim block,blades & risers are:

1. MYLARS: UHMW,Nylon66,PP,Teflon(polytetrafluroethylene (PTFE)).Materials of clamp block and rest block to be decided as per th A class panel or B class.Most of the exterior panel holding Teflon material is used.Sometimes Aluminium blocks also used.
2. CLAMP ARM: SAE 4140 or SAE 1045 .
3. SHIMS/SPACER:S.A.E 1010 CRS FULL HARD COLD ROLLED STRIP STEEL S.A.E.1010 FULL HARD,S.A.E.1020 HRS,etc.
4. SHIM BLOCK:STEEL ASTM A-36,NM STAINLESS,STEEL ASTM A-36,SS TYPE 303 or 304,etc.
5. BLADE:STEEL ASTM A-36,etc.
6. RISER:STEEL ASTM A-36,etc.

HARDNESS:

In general,the hardness of the material for clamp arm,shims,riser,block and blades are:

55-60 HRC/58-62 HRC to a depth of 0.5-0.7mm after grinding.

SURFACE FINISH:

In genral, the hardness of materials for pins,pin retainers,shims,shimblock,blades & riser are:

1. CLAMP ARM:Munsell No.3.75YR6/14 safety orange.
2. SHIMS/SPACER:BLACK OXIDE FINISH (SURFACE TO BE FLAT AND PARELLEL TO WITHIN 0.015MM T.R.I).
3. RISER:SURFACE TO BE FLAT,PARELLEL & PERPENDICULAR TO WITHIN 0.015 T.R.I.

UNIQUE PARTS OF CLAMP CYLINDER:

Finger: Finger is a NC block,which is mounted on the clamp arm of cylinder.And will press the car panel towards the rest,so it holds the car panel.

Rest:A rest is a NC block which is fixed to unit to support the car panel,Also it resists the clamping force of the finger & thus clamp the car panel.

Clamp arm:Clamp arm is a part to which all the movable parts are fixed.In general clamp arms are available as based on the position of arm.They are,

• Middle arm-A10
• Right arm-A11
• Left arm-A12

Clamp cylinder:It is a pneumatic cylinder device works with pressurised air ( 5 bar pressure is standard used to clamp automobile parts).The clamp cylinder is used to open & close the parts fixed to the clamp arm.

1. Clamp cylinders are brought out parts.some of the manufactures are TUNKERS,ZYTRAN,DESTACO,FESTO,STEEL SMITH.
2. Clamp cylinder are generaly 40,50,63 &80 bore capacity ( have to choose as per sheet thickness vs outreach graph).
3. Open upto 135 degrees for horizontal clamp mounting.
4. Open upto 105 degrees for vertical clamp mounting.

DESIGN TREE:

In structure tree all the manufacturing parts should be first and standard parts should be last.structure tree helps to study or understand the parts in the assemblies easily.

CONCLUSION:

Hence as per objective,the three different types of power clamp unit by validating a power clamp cylinder and by considering a clamping force acts at each end of the mylars & three different types of rest unit by considering holding force has been designed ,Also the materials,surface finish & heat treatment used in the parts of clamp unit,purpose of clamp unit & clamp plans are brefily explined in detail.