Industrial Engineering Knowledge Center: Machine Cost and Work Measurement - Time and Cost Estimates for Metal Forming Processes

Wednesday, January 12, 2022

Machine Cost and Work Measurement - Time and Cost Estimates for Metal Forming Processes

Cost estimation is important activity for industrial engineers. For making cash flow estimates for the cost reduction projects or productivity improvement projects, industrial engineers have to prepare cost estimates.

Cost Estimates to Guide Pre-selection of Processes

PDF by AMK Esawi · 2003

https://www.grantadesign.com/download/papers/university/gen6.pdf

Estimation of Forging Cost and Time

Material Estimation for the Forging

Expected Losses in Forging

The losses expected in forging are:

(i) Scale loss.
(ii) Flash loss.
(iii) Tonghold loss.
(iv) Sprue loss.
(v) Shear loss.

(i) Scale loss

When the material used in forging, iron is heated at a high temperature in atmospheric conditions a thin film of iron oxide is formed all round the surface of the heated metal. The iron oxide film falls from the surface of the metal on being beaten up by the hammer. This is termed scale loss and it depends upon the surface area, heating time and the type of material. For forgings under 5 kg, the loss is 7.5 per cent of the net weight, and for forgings from 5 to 12.5 kg and over an addition of 6 per cent and 5 per cent of the net weight is expected as the scale loss.

(ii) Flash loss

This is a loss related to die forging or machine forging.

There is a certain quantity of metal which comes between the flat surfaces of the two dies after
the die cavity has been filled in. This material equal to the area of the flat surface is a wastage. For
finding the flash loss, the circumference is determined which multiplied by cross-sectional area of
flash will give the volume of the flash. The volume multiplied by material density gives the flash loss. Generally, it is taken as 3 mm thick and 2 mm wide all round the circumference.

(iii) Tonghold loss

This is the loss of material due to a projection at one end of the forging to be used for holding it
with a pair of tongs and turning it round and round to give the required cross section in drop forging.
About 1.25 cm and 2.5 cm of the size of the bar is used for tonghold. The tonghold loss is equal to
the volume of the protections. For example, the tonghold volume loss for a bar of 2 cm diameter and tonghold length 2 cm will be (π/4)*2(cube) = 1.25 cm(cube)

(iv) Sprue loss

The connection between the forging and tonghold is called the sprue or runner. The material loss
due to this portion of the metal used as a contact is called sprue loss. The sprue must be heavy
enough to permit lifting the workpiece out of the impression die without bending. The sprue loss is
generally 7.5 per cent of the net weight.

(v) Shear loss

In forging, the long bars or billets are cut into required length by means of a sawing machine.
The material consumed in the form of saw-dust or pieces of smaller dimensions left as defective
pieces is called shear loss. This is usually taken as 5% of the net weight.

Thus nearly 15 to 20% of the net weight of metal is lost during forging. The expected loss of material has to be added to the net weight to get the gross weight of the material.

Forging Cost

The cost of a forged component consists of following elements:
(i) Cost of direct materials.
(ii) Cost of direct labour.
(iii) Direct expenses such as due to cost of die and cost of press.
(iv) Overheads.

(I) Direct material cost

Cost of direct materials used in the manufacture of a forged component are calculated by first determing the net weight based on component drawing and then adding expected losses.

(i) The net weight of forging

Net weight of the forged component is calculated from the drawings by first calculating the
volume and then multiplying it by the density of the metal used.
Net weight = Volume of forging × Density of metal.

(ii) Gross weight
Gross weight is the weight of forging stone required to make the forged component. Gross
weight is calculated by adding expected losses.

Gross weight = Net weight + Material loss in the process.

In case of smith or hand forging, only scale loss and shear loss are to be added to net weight but
in case of die forging other machine related losses are also to be taken into account.

(iii) Diameter and length of stock
The greatest section of forging gives the diameter of stock to be used and
Length of stock = (Gross weight)/[ Sectional area of stock× Density of material]

(iv) The cost of direct metal is calculated by multiplying the gross weight by price of
the raw material
Direct material cost = Gross weight × Price/kg.

(II) Direct labour cost

Direct labour cost = t × l
Where t = Time for forging per piece (in hrs)
l = Labour rate per hour

No general formula is given in books for forging. It has to be estimated internally using time study data of the past.

(III) Direct expenses
Direct expenses include the expenditure incurred on dies and other equipment, cost of using
machines and any other items, which can be directly identified with a particular product.

The method
of apportioning die cost and machine cost:

Apportioning of die cost Let cost of die = Rs. x
No. of components than can be produced using this die be y components
Cost of die/component = Rs. x/y

Apportioning of machine (press) cost

Let cost of press = Rs. A
Life of press be n years

Life of press in hours = B = n × 12 × 4 × 5 × 8 = 1920 n hours
(Assuming 12 months in a year, 4 weeks in a month, 5 days a week, 8 hours of working per day,
Hourly machine price cost of production = A/B
No. of components produced per hour = N
Cost of using press per component = A/ (BN) Rs.

This excludes cost of power consumed and other consumables.

(IV) Overheads expenses

The overheads include supervisory charges, depreciation of plant and machinery, consumables,
power and lighting charges, office expenses etc. The overheads can be expressed as percentage
of direct labour cost or machine hours.

The total cost of forging is calculated by adding the direct material cost, direct labour cost, direct
expenses and overhead.

Three hundred pieces of the bolt are to be made from 25 mm diameter rod. The head has to be 40 mm dia. The length of the head is 22mm and the length of the remaining bolt is 113 mm. Find the
length of material required for forging by upsetting. What length of the rod is required if 4% of the length goes as scrap?

Volume of head of the bolt = (π/4)* D(square)* L

D = 40 mm
L = 22 mm
= (π/4)* 40(square)*22 = 27,646 mm(cube)

Length of material required for making the head
= Volume/area of the blank being used
In the problem the dia. of the blank used is 25 mm

Area = (π/4)* 25(square) = 490.6 mm

∴ Length of bar = 27,632/490.6 = 56.35 mm

Total length required for forming = 56.35 + 113 = 169.35 mm
Length of rod required for making 300 bolts = 169.35*300/1000 = 50.8 metre

Considering loss 4%,
Total length required = (50.8 + .4) × 50.8 = 71.12 metre

Productivity Science and Cost Drivers for Forging

https://www.forging.org/forging/design/331-materials-cost.html

https://www.forging.org/forging/design/332-tooling-costs.html

https://www.forging.org/forging/design/333-manufacturing-cost.html

Manufacturing Cost

Manufacturing cost includes the cost of labor plus the cost of purchasing, maintaining and operating the required machinery and material handling equipment (Machine cost + Labor cost). A portion of these costs is charged to each forging produced. In most cases it also includes the cost of maintaining and replacing the forging tools. Machinery typically includes saws, shears, furnaces, preforming equipment, the forging press or hammer with its associated controls and trim presses. Material handling equipment typically includes cranes, lift trucks, conveyors, etc.

Manufacturing cost of a job is driven by the number of operations required to produce the forging.

Each forging cost center is assigned an hourly operating cost, which is divided by the number of pieces produced per hour to arrive at the cost charged to the forging.

When forging microalloyed steels, which are used to eliminate heat treating, the cost of using special cooling conveyors will be included in the cost of forging. The total manufacturing cost is the sum of the costs of the individual operations used to produce the forging (We can interpret it as a process of producing the forged component and operations involved in the process - operation process chart).

Design simplifications that reduce the number of operations, or reduce the size or complexity of the required forging machines drive toward minimum processing cost. For example, an impression die forging may require several preforming operations, a blocker operation, a finish operation and a trimming operation. The total processing cost is the sum of the costs for each operation. If the design can be modified to reduce the number of operations, processing cost is reduced.

Processing cost can be reduced by designing the forging to facilitate metal flow in the die and reduce forging pressures. This usually involves modifying sharp details to provide larger radii. In some cases it may be possible to use a smaller forging press with a lower hourly operating cost. It is also possible to use machines that produce more parts per hour. Lower forging pressures also tend to reduce tool maintenance and replacement cost, which reduces cost per piece.

Automatic Optimization

Optimization applied to a forging process aims at reducing production costs and improving the quality of the manufactured part. FORGE® and COLDFORM® and SIMHEAT® softwares help in numerical simulation.

WHAT IS AUTOMATIC OPTIMIZATION IN PROCESS SIMULATION?

‘Optimization’ or ‘optimizing’ means running a series of simulations to identify the ideal process conditions giving the best final result.

Optimization follows a number of set parameters:

Objective: billet weight, die wear or die stress, tonnage, difference with experimental plots, etc. The objective can be to minimize or to maximize.

Process conditions: billet size or position, lubricant, temperature, die geometry, etc.

Constraints to respect (additional mandatory condition): complete filling of the die cavity, no folds or laps, prescribed scalar value, prescribed force or torque value, etc.).

HOW DOES IT WORK?

Automatic Optimization is based on MAES methods (Metamodel-Assisted Evolution Strategies) proposed by Emmerich et al. It has shown its efficiency and robustness in several complex metal forming applications.

Each simulation uses a set of process parameters (diameter and length) and is referred to as an ‘individual’. Each ‘generation’ includes several individuals. Good individuals match the objective and respect the constraints. Poor individuals do not respect the constraints. The next generation is automatically based on the best current individuals. The algorithm loops until the given number of generations has been reached. At each generation, a new population of individuals is created. A cost-function is used to rank each individual and designate the ‘best candidate’.

Defining a Design of Experiment (DOE), the user indicates to the system a selection of values (process conditions) to be tested. Combining Automatic Optimization based on Metal Model Design with the DOE is a good technique to find the solution.

https://www.transvalor.com/en/blog/automatic-optimization-of-forging-processes

The Activity-based Costing Approach for Estimation of Cost of a Forged Part`s in FMS with A(2)-Degree Automation: A Case Study in a Forging Industry

K. Rezaie and B. Ostadi

Information Technology Journal

Year: 2006 | Volume: 5 | Issue: 3 | Page No.: 546-550

DOI: 10.3923/itj.2006.546.550

https://scialert.net/abstract/?doi=itj.2006.546.550

COMPUTERIZED COST ESTIMATION FOR FORGING - PDF

In this study, an interactive cost estimation software named “Forge Cost. Estimator”, which performs the early cost estimation for forgings, has been developed.

https://etd.lib.metu.edu.tr/upload/4/1060193/index.pdf

Estimation of Forging Die Wear and Cost - THESIS PDF

Knight‟s Cost Model. Knight developed a cost model to estimate die costs for hammer forging

https://etd.ohiolink.edu/apexprod/rws_etd/send_file/send?accession=osu1277993083&disposition=inline

Open Access

Published: 29 August 2020

An analytical cost estimation model for the design of axisymmetric components with open-die forging technology

Federico Campi, Marco Mandolini, Claudio Favi, Emanuele Checcacci & Michele Germani

The International Journal of Advanced Manufacturing Technology volume 110, pages1869–1892 (2020)

Abstract

Open-die forging is a manufacturing process commonly used for realising simple shaped components with high mechanical performances and limited capability in terms of production volume. To date, an analytical model for estimating the costs of components manufactured with this technology is still an open issue. The paper aims to define an analytical model for cost estimation of axisymmetric components manufactured by open-die forging technology. The model is grounded on the analysis of geometrical features available at the design stage providing a detailed cost breakdown in relation to all the process phases and the raw material. The model allows predicting product cost, linking geometrical features and cost items, to carry out design-to-cost actions oriented to the reduction of manufacturing cost.

Cost model and related schemas for collecting equations and data are presented, including the approach for sizing the raw material and a set of rules for modelling the related cost. Finally, analytic equations for modelling the cost of the whole forging process (i.e. billet cutting, heating, pre-smoothing, smoothing, upsetting, max-shoulder cogging, necking and shoulders cogging) are reported. The cost model has been tested on eight cylindrical parts such as discs and shafts with different shapes, dimensions and materials. Two forge masters have been involved in the testing phase. The absolute average deviation between the actual and estimated costs is approximately 4% for raw material and 21% for the process. The absolute average deviation on the total cost (raw material and manufacturing process) is approximately 5%.

https://link.springer.com/article/10.1007/s00170-020-05948-w

Forging - Introduction Material

https://manufacturing-videos.blogspot.com/2019/08/forging-introduction.html

Updated 12 Jan 2022, 21 May 2021

Pub 29 Nov 2019