Daily Archives: January 8, 2021

What effects does friction have on a forminglimit diagram?

1.What effects does friction have on a forminglimit diagram? Explain. By the student. Friction can have a strong effect on formability. High friction will cause localized

 

strains, so that formability is decreased. Low friction allows the sheet to slide more easily

over the die surfaces and thus distribute the strains more evenly.

2.Why are lubricants generally used in sheetmetal forming? Explain, giving examples.

Lubricants are used for a number of reasons. Mainly, they reduce friction, and this improves

formability as discussed in the answer to Problem

 

How would you produce the parts shown in Fig. 7.35b other than by tube hydroforming?

1.How would you produce the parts shown in Fig. 7.35b other than by tube hydroforming?

 

By the student. The part could be produced by welding sections of tubing together, or by a

suitable casting operation. Note that in either case production costs are likely to be high and production rates low.

2. Give three examples each of sheet metal parts that (a) can and (b) cannot be produced by

incremental forming operations. By the student. This is an open-ended problem

that requires some consideration and creativity on the part of the student. Consider, for example: (a) Parts that can be formed are light fixtures,

automotive body panels, kitchen utensils, and hoppers.

(b) Incremental forming is a low force operation with limited size capability (limited

to the workspace….

Explain why a metal with a fine-grain microstructure is better suited for fine blanking than a coarse-grained metal.

Explain why a metal with a fine-grain microstructure

 

is better suited for fine blanking

than a coarse-grained metal.

A fine-blanking operation can be demanding;

the clearances are very low, the tooling is elaborate

(including stingers and a lower pressure

cushion), and as a result the sheared surface

quality is high. The sheared region (see Fig. 7.6

on p. 353) is well defined and constrained to

a small volume. It is beneficial to have many

grain boundaries (in the volume that is fracturing)

in order to have a more uniform and

controlled crack.

Review Eqs. (7.12) through (7.14) and explain which of these expressions can be applied to incremental forming. By the student. These equations are applicable because the deformation in incremental forming is highly localized. Note that the strain relationships apply to a shape as if a mandrel was present. 7.63 Referring to Eq. (7.5), it is stated that actual values of eo are significantly higher than values of ei, due to the shifting of the neutral axis during bending. With an appropriate sketch, explain this phenomenon. The shifting of the neutral axis in bending is described in mechanics of solids texts. Briefly, the outer fibers in tension shrink laterally due to the Poisson’ effect (see Fig. 7.17c), and the inner fibers expand. Thus, the cross section is no longer rectangular but has the shape of a trapezoid, as shown below. The neutral axis has to shift in order to satisfy the equilibrium equations regarding forces and internal moments in bending.

Review Eqs. (7.12) through (7.14) and explain which of these expressions can be applied to incremental forming. By the student. These equations are applicable because the deformation in incremental forming is highly localized. Note that the strain relationships apply to a shape as if a mandrel was present. 7.63 Referring to Eq. (7.5), it is stated that actual values of eo are significantly higher than values of ei, due to the shifting of the neutral axis during bending. With an appropriate sketch, explain this phenomenon. The shifting of the neutral axis in bending is

 

described in mechanics of solids texts. Briefly, the outer fibers in tension shrink laterally due to the Poisson’ effect (see Fig. 7.17c), and the inner fibers expand. Thus, the cross section

is no….

cut the blank from paper and verify that the tray is As such, the important factors are bendability, and scoring such as shown in Fig. 7.71

The design shown in the accompanying illustration is proposed for a metal tray, the main body of which is made from cold-rolled sheet steel. Noting its features and that the sheet is bent in two different directions, comment on relevant manufacturing considerations. Include factors

 

such as anisotropy of the cold-rolled sheet, its surface texture, the bend directions, the nature

of the sheared edges, and the method by which the handle is snapped in for assembly.

By the student. Several observations can be made. Note that a relief notch design, as shown

in Fig. 7.68 on p. 405 has been used. It is a valuable experiment to have the students cut

the blank from paper and verify that the tray is As such, the important factors are….

Design a box that will contain a 4 in. × 6 in. × 3 in. volume.

Design a box that will contain a 4 in. × 6 in. × 3 in. volume. The box should be produced from two pieces of sheet metal and require no tools or fasteners for assembly. This is an open-ended problem with a wide variety of answers. Students should consider the blank shape, whether the box will be deepdrawn or produced by bending operations (see Fig. 7.68), the method of attaching the parts (integral snap-fasteners, folded flaps or loosefit),

 

and the dimensions of the two halves are all variables. It can be beneficial to have the

\students make prototypes of their designs from cardboard. 7.100 Repeat Problem 7.99, but the box is to be made from a single piece of sheet metal.

This is an open-ended problem; see….

Explain why scalloping occurs.

In opening a can using an electric can opener, you will note that the lid often develops a scalloped periphery. (a) Explain why scalloping occurs. (b) What design changes for the can

 

opener would you recommend in order to minimize or eliminate, if possible, this scalloping

effect? (c) Since lids typically are recycled or discarded, do you think it is necessary or worthwhile to make such design changes? Explain. By the student. The scalloped periphery is

due to the fracture surface moving ahead of the shears periodically, combined with the loading

applied by the two cutting wheels. There are several potential design changes, including

changing the plane of shearing, increasing the speed of shearing, increasing the stiffness of the

support structure, or using more wheels. Scallops on….

prepare a brief technical paper on this topic.

A recent trend in sheet-metal forming is to provide a specially-textured surface finish that develops small pockets to aid lubricant entrainment. Perform a literature search on this technology, and prepare a brief technical paper on this topic.

 

This is a valuable assignment, as it encourages the student to conduct a literature review.

This is a topic where significant research has been done, and a number of surface textures

are available. A good starting point is to obtain the following paper:

Hector, L.G., and Sheu, S., “Focused energy beam work roll surface texturing science and

technology,” J. Mat. Proc. & Mfg. Sci., v. 2, 1993, pp. 63-117.

demonstrate the competencies required to design, plan and deploy virtualization solutions.

Virtualization Assessment Part 1

About this assessment

These assessment tasks provide an opportunity to demonstrate the competencies covered in the Virtualization subject.

 

You are allowed to refer to your text books, notes and the Internet during the Assessment. You are required to complete all the tasks with in the allowed time to be successful in this assessment The documentation and research work must be entirely your own.

Successful completion of this assessment contributes towards attaining competency in the following:

 

ICTSUS501 Implement server virtualisation for a sustainable ICT system ICTNWK525 Configure an enterprise virtual computing environment ICTNWK535 Install an enterprise virtual computing environment

ICTICT511 Match IT needs with the strategic direction of the enterprise

These assessment tasks provide an opportunity for you to demonstrate the competencies required….

explain what would happen to the forecasts in this case.

(g) Suppose now that the researcher had estimated the above GARCH model for a series of returns on a stock index and obtained the following parameter estimates: µˆ = 0.0023, aˆ 0 = 0.0172,

ˆß = 0.9811, ˆa1 = 0.1251. If the researcher has data available up to and including time T , write down a set of equations in s2 t and u2t their lagged values, which could be employed to produce one-, two-,

and three-step-ahead forecasts for the conditional variance of yt .

(h) Suppose now that the coefficient estimate of ˆß for this model is 0.98 instead. By re-considering the forecast expressions you derived in part (g), explain what would happen to the forecasts in this case.