Week 6:- Clamp Unit & Pin-Clamp Unit Design Challenge
- Design 3 Different types of Swivel Clamp Unit with Different Riser, Blade and Clamp Arm for the given Car Panel.
- Design a Pin-Clamp unit for the given Car Panel.
Aim/Introduction/ Objective: In this challenge we have to Design 3 Different types of Swivel Clamp Unit with Different Riser, Blade and Clamp Arm for the given Car Panel & Design a Pin-Clamp Unit for the given Car Panel with the optimum use of material & space constraint also considering panel thickness as 1 mm for this unit.
Report & theory:
3-2-1 principle achievement:
3-2-1 principle is basis of any fixture design. Holding fixtures used in assembly operations often follow a 3-2-1 locating scheme to position parts. Under this scheme, three locators position a part in a primary plane or direction (e.g., high/low).
(3) minimum: Three locator blocks to establish part plane. Three locators or supports are placed under the work piece. Three locators are usually positioned at primary locating surfaces. This restrict two translation motion i.e. upward & downward & four rotational motion ( i.e. clockwise or anticlockwise). Together tree locators with clamp restrict six degrees of freedom. Below figure shows how (3) minimum in 3-2-1 locating scheme achieved by clamping & resting.
(2) Round locating pin in a round hole that defines location in four directions (4 ways) perpendicular to the plane previously established. This restricts four axial movements
With the four Swivel clamp unit restrict four rotational motion & two translation motion as shown in below figure. With the use of pin unit we restrict four translation motion. Together we restrict 10 degrees of freedom.
Clamp unit: Clamp unit is unit designed to clamp / hold the car panel with NC blocks/ mylar/ rest by using a pneumatic clamp cylinder & below are different parts of a clamp unit in general. Usually clamp open position is 90°. Fingers are attached to clamp mylar. In clamp unit shim to one side is more enough because it will restrict translation motion in upward & downward direction only. There is another type of clamp unit knows as swivel type. There is pivot pin around which clamp arm rotate.
Factors should be considered while designing a clamp unit:
- There should be adequate space between the cylinder & another part like riser, car panel because cylinder moves or swing while opening & closing
- Pin clamp unit used where two panel or component are located for welding.
- Clamping make in such way that it clamps two car panels at once
- All parts should snap & butt properly to each other.
- Make sure that parts of the clamping unit are 10 to 12 mm away from car panel so they do not damage car panel
- Avoid any clash. It will not arises issue at assembly.
Below are general parts of swivel clamp unit.
a) Clamp Cylinder:
Cylinder designation: In this unit we used Clevis cylinder for clamping designated as CKG_1B_63_100Y
Nomenclature of cylinder as belows:
CKG1: Series of cylinder
B: Clevis width as 19.5 mm.
63: Bore size
100: Stroke of cylinder
Y: End bracket i.e. double knuckle joint (M6 without tap)
b) Clamp arm: It is part to which clamp mylar mounted & also clamp cylinder is attached to the end of arm with the use of clevis pin. It has two plates of 8 mm thickness welded & helps in rotating of clamp arm about pivoting point of blade.
- The distance between cylinder rod hole & pivoting hole should be 50 mm as shown in figure. This is necessary because cylinder stroke 100 mm must be achieved when it is at 90° open position & clamp arm mounting hole must be in line with cylinder rod axis as shown in below figure
Below figure shows 100 mm stroke achieved & clamp arm end in line with cylinder rod. See Y & Z values.
- Sharpe edges must be removed. Chamfer or fillet always provided for aesthetic & safety purpose.
c) Mylar/ NC blocks/ Fingers: These are parts are used to hold panel. They are globally called as Mylar. Top side Mylar is called as clamping Mylar & bottom side is called resting Mylar. Every clamping Mylar should have resting Mylar. It is jaw type. It prevent panel from deforming while welding. It is hardened to increase its wear strength. Following consideration should be taken into account while designing Mylar.
- The clamp & rest Mylar has the same size. It has standard size of 20mm x20mm. It has flat surface or sometimes its profile follow contour of car panel. As described in below figures.
- Clamp & rest mylar have two dowel holes of dia.6 & one M8 tapping hole. Also clamp mylar have same mounting hole pattern as like clamp arm. Also minimum centre distance between holes should be 15 mm. & reference dimension should be 8 or 10 mm. as described in below figure.
- Minimum distance between clamp mylar mounting face & car panel should be more than 5 mm
d) Stopper:
The function of stopper is to restrict motion of clamp arm. It avoids clamp arm to rotate beyond limit. It has two parts male & female.
e) Blade: Blade is part to which all other units are attached for e.g. mylar, stopper, clamp cylinder, riser. Blade is designed according to position of all other parts.
Below figure shows how other parts are mounted on blade.
f) Riser: Risers can be of L-type, welded or square tube or frame type. These are basically manufactured parts are used to give height to assembly. It is machined at mounted ends only to save cost.
g) Bush: Bush is friction type bearing. It is lubricated with grease, oil. It permits relative motion between two mating parts. It is made of hard material also its ID & OD are precisely machined or grinded. It press fitted & after worn out it is replaced with new one instead of replacing other part which save cost. Mostly phosphor bronze or gun metal material used for making bush. In this unit three bushes are used of same internal (12 mm) & external diameter (18 mm) but different length.
h) Shims/spacer: In fixture, we are providing tolerance to each part mostly manufactured. Those tolerances tend to stack up & reflect together. In order to avoid that we use shims so we can easily adjust after assembly so whatever stack up there we will rectify it through shims. Shims come in thickness of 0.1, 0.2, 0.5 etc.
We provide shim to accommodate clamp as well as rest mylar in two direction. Clamp & rest mylar can be adjusted in one direction only i.e. up or down. Also two way shim provided for locating pin to accommodate adjustment.
h) Hardware: These are standard parts. Parts are assembled together with help of washer and bolt. for better assembly should use two dowels and four bolts for riser and blade. Where for bolting one part should have tapping hole and on other part simple hole (1 to 2 mm larger from bolt size.)
Length of the bolt is decided by width of part + (1.5*D)
For ex. where
L=Length of Bolt
D=diameter of bolt to be used
Let’s, take M8 Bolt
L= 25 + (1.5 * 8)
L=25+12
L=37 mm.
But length of 37mm bolt is not available so we have to select 40mm Bolt. (Additional 2 to 3 for washers).
Similarly minimum engagement length for M5, M6, M10 & M12 must be 7.5, 9, 15, 18 mm respectively.
j) Dowel pins: These are standard part. There are various types of dowel pin like split, parallel, taper, clevis, and spring, grooved. Dowel pins are used to locate part precisely & to restrict movements. For mylar dia. 6 or 8 dowel pins should be used. For blade, shimming block dia.8 dowel pin should be used & for riser base dia. 10 or 12 pins are used.
k) Washer: Standard steel grade A plain normal series washer used.
Below are 3 designed Swivel clamp unit & one pin clamp unit:
Below unit is named as P001_Z01_ST006_01_00_SWIVEL_CLAMP_UNIT & is designed with Clevis clamp cylinder.
Below fig shows clamping of car panel & also retracted position of clamp arm at 90°.
Below unit is named as P001_Z01_ST006_02_00_SWIVEL_CLAMP_UNIT & is designed with Clevis clamp cylinder.
Below unit is named as P001_Z01_ST006_03_00_SWIVEL_CLAMP_UNIT & is designed with Clevis clamp cylinder.
Below unit is named as P001_Z01_ST006_04_00_PIN_CLAMP_UNIT & is designed with Clevis clamp cylinder.
Below figure shows clamp units with car panel.
In below figure, Red box shows a yellow part (open position) which will not intersect panel while loading & unloading.
Below figure shows clamp units without car panel.
Clamp plan: It provides information about position of clamp unit, pin unit, rest unit, dump unit etc. This is major input from customer & it should be never changed without permission of customer. Clamp plan provide exact location of pins, rest, clamp etc. It is in more detail. It gives exact location in X, Y & Z co-ordinates value to start designing.
Structuring a design tree:
Structuring a design tree implies process where all the assemblies & parts are named in specific manner. Different customers have different set of standard like how to structure a design tree? So they will be give standard template based on that design tree structured, which helps us to identify specific part of assembly. It specifies the Project number, station number, unit number; part number of each component so that it is easy to identify the parts.
It is an important process which helps us to identify a specific part or assembly as to which project, tool or unit, it belongs to.
This helps us to avoid error during design study, manufacturing, assembly, inspection etc.
If parts or assemblies are not named properly or the design tree is not structured properly, it will create confusion to understand & create major possibilities of making an error.
Naming of a fixture, a unit or a part gives the information as to which project or zone or assembly they do belong.
It can help us to identify quantity of items of same type or different types that are being used in assembly for e.g. bolt. It actually tells you how many bolts are particularly required in that assembly or unit.
For e.g. as in below figure highlighted in blue
P001 stands for project no 1.
Z01 stands for zone no 1.
ST006 stands for station no 6.
01 stands for unit no. e.g. Swivel clamp unit
01 stands for part no. e.g. Rest mylar