chapter 4 & 5

Design and analysis of combination press tool for c shaped clamp

CHAPTER 4

PRESS TOOL DESIGN

Tool design is a specialized area of manufacturing engineering comprising of analysis, planning,

design, construction and application of tools, methods and procedures necessary to increase

manufacturing productivity. Making a good die begins with die designer. If the die is designed is

correctly it will work properly and require infrequent, simple repairs. The design process

basically consists of five steps.

1 Statement and analysis of the problem.

2 Analysis of the requirement.

3 Development of initial ideas.

4 Development of design alternatives.

5 Finalization of design ideas.

4.1 Design of Combination Press Tool Elements

1. Strip layout (material utilization).

2. Force required.

Cutting or Shearing force required.

Stripping force required.

Bending force required.

Press force required.

3. Press tool elements calculation.

Cutting clearance.

Thickness of die plate.

Thickness of die back plate.

Thickness of bottom plate.

Thickness of top plate.

Thickness of stripper plate.

Thickness of punch holder.

Thickness of punch back plate.

Department of Mechanical Engineering, R.V.C.E M-Tech tool Engineering


Length of piercing punch.

The Maximum Length of a punch.

4.2 Study of Component ClampComponent study is the first step in tool design process. Component study gives the details about

the material to be used properties and application of the component. It also helps in identifying

the critical dimensions related to the component which has to be achieved; hence more emphasis

can be given to such areas while designing the tool. Figure 4.1 gives the details of component for

which a combination tool needs to be designed. Table 4.1 gives the component specifications and

its properties.

2D drawing of clamp

Table 4.1 Component Hinge specifications

Details Specification

Material Stainless Steel 409L

Thickness 1.5mm

Chemical composition Carbon : 0.012%, Nickel : 0.15%, Chromium :

21.5%, Molybdenum : 0.030 % Nitrogen:

0.009%

Shear strength 400 N/mm²

Ultimate Tensile strength 500 N/mm²

4.3 Blank Development of clampIn the Hinge, the curled portions were unwrapped to establish the sequence of operations and

dimensions of the strip required. The sequence of operations on a strip and details of each

operation must be carefully developed to ensure the safe design. Calculation of bending

allowance is essential to estimate the required flat work piece length to make a bend. The curved

neutral plane of the bend area is the bend allowance. To make a bend as shown in the Fig. 4.1 the

length of the blank is determined as follows.

L = L1 + L2 + A,

Where,



L= Length of the flat blank required to make bend (mm)

L1= Length of bend leg1 (mm)

L2= Length of bend leg2 (mm)

A= Bend allowance (mm) = [(π*θ) ÷ 180⁰] * [IR + (k*t)]

θ- Area of bend,

k- Correction factor= 0.33 if R<2t.

Fig. 4.2 Bend allowance [53]

Bend developed length of hinge when curls were unwrapped as shown in Fig 4.3 is determined

as follows:

DEVELOPED LENGTH

L1 = 21.5mm

L2 = πA/180(I.R + Kt/2)

= πx90/180(4 + 0.5x1/2)

L2= 7.06mm

Where,



A = Angle of bendI.R= Internal radiusK = Correction factor

Limits of KR≥2t = 0.5R≤2t = 0.3

L3 = 10mm L4 = πA/180(I.R + Kt/2) = πx180/180(12.5+0.5x1/2)L4 = 40.84mm

L5 = L3 = 10mm

L6 = L6 = 7.06mm

L7 = 21.5mm

Total length = L1+L2+L3+L4+L5+L6+L7

= 21.5+7.06+10+40.84+10+7.06+21.5 = 117.96mm ≈ L = 118mm

Fig 4.3 Blank development of clamp

4.4 Strip Layout (material Utilization)In the design of blanking parts from a strip of material, the first step is to prepare the layout, that

is, to layout the position of the work pieces in the strip and their orientation with respect to one

another. While doing so, the major consideration is the economy of material. Another important

consideration in strip layout is the distance between the blanks and the strip edge and distance

between blank to blank.

The different types of strip layout are

1. Narrow run

2. Wide run

3. Angular run

The formula used to calculate material utilization.



% Area of utilization = Area of blank x No of rows x 100 Pitch x Strip width

= (2520 × 1/21.5 × 125)100 = 95.29%

4.5 Force Required Calculation

4.5.1 Cutting or Shearing force calculation (Fs)

Piercing (S.F) 1

(S.F) 1 = L1 × t × Fs L1 = π×D = 31.4 × 1 × 40.77 = π(5) × 2 (S.F) 1 = 1.28T = 31.4mm

Where, t = thickness of sheet (mm) D = diameter of hole (mm) FS= shear strength (kg/mm2)

Blanking (S.F) 2 (S.F) 2 = K×L2×t×FS

1000 = 1.2 × 280 × 1 × 40.77 1000 (S.F) 2= 14TWhere, K = Factor of Safety L2 = Cut length (mm) t = Thickness (mm) FS = Shear Strength (kg/mm2)

4.5.2 Bending Force (Fb)



Fb = k × L × Su × t2

W = 2.66 × 20 × 50 × 12

27 Fb = 0.098T

Where,

k = die opening factor

For ‘U’ bending

k= 2.66 for W= 8t k= 2.40 for W= 16t L= distance between supports (mm) Su= ultimate tensile strength (kg/mm2) W= width of dent up portion (mm)

Bending force (thumb rule) (Fb)

Fb = 20%of cutting force = 0.2 × 15 Fb = 3T

4.5.3 Stripping force Calculation

S = (L × t × Fs) x 0.20

= 2802 × 40.77 × 0.20 1000 S = 2.25TWhere,

S = stripping force (T) t = material thickness (2mm) L= total cutting length (280mm) Fs= Shear strength (40.77kg/mm2)

4.5.4 Press force (P)

P = S.F1 + S.F2 + Fb + S = 1.28 + 14 + 3 + 2.25 P = 20.53T Safety= 25%press force



= 0.25(21) = 5T

Total force required (F) F = Press force + Safety = 21 + 5 F= 26T

The press selected was 63T SNX press.

4.6 Press Tool Calculation

4.6.1 Calculation of cutting clearance

Cutting clearance (c)

Formula method = 0.005t √Fs

= 0.005 ×1×√40.77 = 0.03mm/side Percentage method = 5% of sheet thickness = 0.05 × 1

= 0.05mmWhere, t = thickness (mm) Fs=shear strength (kg/mm2)

4.6.2 Thickness of die plate

Td = 3√F = 3√30

= 3 cm≈ Td = 40mm

The plate selected was 40mm as it was the nearest standard available.

4.6.3 Thickness of die back plate

Tdbp = (0.5~0.8) Td

= 0.5 × 40 Tdbp = 20mm

The standard 20mm plate was selected.



4.6.4 Thickness of bottom plate

Tbp = (1.25~1.75) Td

= 1.25 × 40 Tbp = 50mm


4.6.5 Thickness of top plate

Ttp = (1.25~1.75) Td

= 1.25 × 40 Ttp = 50mm


4.6.6 Thickness of stripper plate

Tsp = (0.6~0.8) Td

= 0.6 × 40 = 24mm≈ Tsp= 30mm


4.6.7 Thickness of punch holder

Tph = (0.6~0.8) Td = 0.6 × 40 = 24mm≈

Tph = 30mm


4.6.8 Thickness of punch back plate

Tpbp = (0.5~0.8) Td

= 0.5 × 24 = 12mm≈Tpbp = 20mm


4.7 Types of fits used in Press Tool



When two parts are to assemble, the relation resulting from the difference between the sizes

before assembling is called fit. A machine part when manufactured has a specified tolerance.

Therefore, when two mating parts fit with each other, the nature of fit is dependent on the limits

of tolerances and fundamental deviations of the mating parts. The types of fits employed in this

tool are described in the table 4.5 given below.

Table 4.5 Fits used in press tool

Sl no: Tool Elements Type of fit1 Blanking punch and Stripper H7/g6 (sliding fit)

2 Piercing punch and Stripper H7/g6 (sliding fit)3 Guide pillar with Bottom plate H7/p6 (press fit)4 Guide pillar with Guide bush H7/g6 (sliding fit)

5 Punch with Punch holder H7/k6 (light key fit)

6 Pilot with Stripper H7/g6 (sliding fit)

7 Direct Pilot with Punch H7/p6 (press fit)

8 Pilot with Punch holder H7/k6 (light key fit)

9 Dowels with stripper plate H7/m6 (medium drive fit)

10 Dowels with Die plate H7/m6 (medium drive fit)

11 Dowels with Bottom plate H7/m6 (medium drive fit)

12 Dowels with Top plate H7/m6 (medium drive fit)

13 Dowels with Punch holder plate H7/m6 (medium drive fit)

14 Stopper with die plate H7/k6 (light key fit)

15 Guide bush with Top plate H7/p6 (press fit)

16 Finger stopper and slot in Stripper plate H7/g6 (sliding fit)

17 Punch and Die Cutting clearance fit

4.8 Machine specification

The specifications of a 63T machine which can withstand the calculated press tonnage are given

in Table 4.4 below. The schematic sketch of ‘C’ frame press machine with terminology and a

photograph of SNX63 press machine are shown in the fig 4.8(a) and 4.8(b) below.



Fig 4.8(a) schematic sketch of ‘C’ frame press machine [10]

Fig 4.8(b) Press machine SNX63 [courtesy: Adithya Tools, NTTF]Table 4.2 Machine specification

Model SNX63

Tonnage (T) 63

Strokes per minute (SPM) 100



Die height (mm) 300

Tool bore (mm) 50.8

Bolster area (mm2) 900×520

Bolster thickness (mm) 120

Floor to top of bolster (mm) 870

Main motor (H.P) 7.5

4.9 PRESS TOOL DESIGN

4.9.1 2-Dimensional Drawings of combination Press Tool

4.10 Summary

This chapter describes the preparation of strip layout for hinge, calculation of shearing, bending,

stripping, and press force required, determination of cutting clearance required between punch

and die and design of press tool elements are determined. The specifications of the machine to be

accommodated are also discussed in this chapter. The 2 D drafting and 3D modelling are also

shown in this chapter. The importance of above calculations is explained within it. The materials

selected are given in bill of material for top half, bottom half and standard items as shown in

Appendix I.

CHAPTER 5

FINITE ELEMENT ANALYSIS OF PRESS TOOL ELEMENTS



Finite element analysis (FEA) is a computerized method for predicting how a product reacts to

real-world forces, vibration, heat, fluid flow, and other physical effects. Finite element analysis

shows whether a product will break, wear out, or work the way it was designed. It is called

analysis, but in the product development process, it is used to predict what is going to happen

when the product is used.

FEA works by breaking down a real object into a large number (thousands to hundreds of

thousands) of finite elements, such as little cubes. Mathematical equations help predict the

behavior of each element. A computer then adds up all the individual behaviors to predict the

behavior of the actual object.

5.1 Structural analysis of Punches and Die InsertsThe objective of carrying out structural analysis on punches and die inserts was to determine

whether the stress, strain and shear stress induced in punches and die inserts as a result of the

load applied was within the permissible limit.

5.2 Types of Engineering AnalysisThe different types of engineering analysis are.

Structural analysis consists of linear and non-linear models. Linear models use simple

parameters and assume that the material is not plastically deformed. Nonlinear models

consist of stressing the material past its elastic capabilities.

Vibration analysis is used to test a material against random vibrations, shock, and

impact. Each of these incidences may act on the natural vibration frequency of the

material which, in turn, may cause resonance and subsequent failure.

Fatigue analysis helps designers to predict the life of a material or structure by showing

the effects of cyclic loading on the specimen. Such analysis can show the areas where

crack propagation is most likely to occur. Failure due to fatigue may also show the

damage tolerance of the material.

5.3 Finite Element Analysis of Punches

5.3.1 Piercing punch



Fig 5.1 Piercing punch

Element type: Tetrahedrons

Element size: 1 mm

Applied load: 6300 N

Area: 19.63 mm2

No of nodes: 1142

No of elements: 543

Equivalent (Von-Mises) Stress

Fig 5.2 Equivalent (Von-Mises) Stress in piercing punch

Equivalent Strain



Fig 5.3 Equivalent Strain in piercing punch

Shear stress

Fig 5.4 Shear stress in piercing punch

Table 5.1 Piercing punch ANSYS results



Objective Maximum Minimum

Equivalent (Von-Mises) Stress 320.22MPa 12.965MPa

Equivalent Strain 0.0016462 0.000122

Shear stress 158.71MPa -554.57MPa

5.3.2 Blanking punch

Fig 5.5 Blanking punch


Element size: 1 mm

Applied load: 134400N

Area: 2320 mm2

No of nodes: 5100

No of elements: 2925




Fig 5.6 Equivalent (Von-Mises) Stress in blanking punch

Equivalent Strain

Fig 5.7 Equivalent strain in blanking punch

Shear stress



Fig 5.8 Shear stress in blanking punch

Table 5.2 Blanking punch ANSYS results



Equivalent Strain 3.3x10-4 1.7x10-5


5.3.3 Bending punch



Fig 5.9 Bending punch


Element size: 1 mm

Applied load: 30,000N

Area: 1614 mm2

No of nodes: 3803

No of elements: 2098




Fig 5.10 Equivalent (Von-Mises) Stress in bending punch

Equivalent Strain

Fig 5.11 Equivalent strain in bending punch

Shear stress



Fig 5.12 Shear stress in blanking punch

Table 5.3 Bending punch ANSYS results



Equivalent Strain 2.4x10-4 2.5x10-6


5.4 Theoretical Calculation



5.4.1 Piercing punchUnit Stress (σ) = force/ area =6300/19.63 = 320.8 MPa

Unit Strain (e) = stress/ Young’s modulus = 320.8 / 210 x 103 = 1.604x10-3

Maximum shear stress(τ) =(1/2) x Equivalent (Von-Mises) Stress =329.22/2 = 164.61MPa

5.4.2 Blanking punchUnit Stress (σ) = force/ area =134400/2320 = 57.93 MPa

Unit Strain (e) = stress/ Young’s modulus = 57.93/ 210 x 103 = 2.8x10-4


5.4.3 Blanking punchUnit Stress (σ) = force/ area =29430/1614 = 18.39 MPa

Unit Strain (e) = stress/ Young’s modulus = 18.39/ 210 x 103 = 6.1x10-5


5.5 Results



The comparison of analysis and theoretical results are tabulated in the below table 5.4 shows the results.

Table 5.4 Results

Sl. no. Description Analysis result Theoretical result

1. Piercing punch

Stress 329.22MPa Stress 320.8MPa

Strain 1.6x10-3 Strain 1.60x10-4

Shear stress 158.71MPa Shear stress 164.61MPa

2. Blanking punch




3. Bending punch




5.6 SummaryFinite element analysis of press tool elements deals with determination of stresses, strains and

shear stresses induced in punches for the load applied. Analysis was carried out in ANSYS work

bench 14 software and Solid 187 element was used for meshing of punches. After the Finite

element analysis was carried out on the critical elements of press tool it was observed that the

resultant stress and strain values were well within the allowable yield stress (i.e. 1650 Mpa) of

the material. The results obtained from Finite element analysis were compared with theoretical

values and were found to be approximately nearer. Table 5.4 shows the results.


chapter 4 & 5

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