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<span class='text_page_counter'>(1)</span>ECONOMIC AND PRODUCT DESIGN CONSIDERATIONS IN MACHINING Machinability Tolerances & Surface finish Selection of cutting conditions Product design considerations.

<span class='text_page_counter'>(2)</span> Selection of cutting conditions. ECONOMIC AND PRODUCT DESIGN CONSIDERATIONS IN MACHINING. Selecting feed & depth of cut Optimizing cutting speed.

<span class='text_page_counter'>(3)</span> SELECTING FEED AND DEPTH OF CUT Cutting speed. Feed rate Cutting conditions. depth of cut. cutting fluid.

<span class='text_page_counter'>(4)</span> SELECTING FEED AND DEPTH OF CUT. often predetermined by workpiece geometry and operation sequence. DEPTH OF CUT. In the roughing operations, depth is made as large as possible within the limitations of available horsepower, machinetool and setup rigidity, strength of the cutting tool, and so on In the finishing cut, depth is set to achieve the final dimensions for the part.

<span class='text_page_counter'>(5)</span> SELECTING FEED AND DEPTH OF CUT. Tooling. Feed rate. Roughing or finishing Constraints on feed in roughing Surface finish requirements in finishing.

<span class='text_page_counter'>(6)</span> OPTIMIZING CUTTING SPEED. CUTTING SPEED. Selection of cutting speed. • Based on making the best use of the cutting tool, which normally means choosing a speed that provides a high metal removal rate yet suitably long tool life. Cutting Maximum production rate speed Minimum unit cost.

<span class='text_page_counter'>(7)</span> OPTIMIZING CUTTING SPEED • the time the operator spends loading the Part part into the machine tool at the beginning handling of the production cycle and unloading the time part after machining is completed Maximizing Production Rate (in turning). Machinin • the time the tool is actually engaged in g time machining during the cycle. Tool change time. • At the end of the tool life, the tool must be changed. This time must be apportioned over the number of parts cut during the tool life.

<span class='text_page_counter'>(8)</span> OPTIMIZING CUTTING SPEED. Tc. The sum of these three time elements gives the total time per unit product for the operation cycle. �� � � =� h +� � + �� : the number of pieces cut in one tool life. Machining time in a straight turning operation is given by previous. � �� � �= ��.

<span class='text_page_counter'>(9)</span> OPTIMIZING CUTTING SPEED. �. �� =� � �� � �= �� � �� = ��. �� =. ��. 1 �. � ���. 1 �− 1. (. � �� � � � ��� � �=� h + + 1 �� � ��. 1 �−1. ).

<span class='text_page_counter'>(10)</span> OPTIMIZING CUTTING SPEED. The cycle time per piece is a minimum at the cutting speed is zero. �� � =0 ��. Solving. � ��� =. �. [(. 1 −1 �� �. ). �. ].

<span class='text_page_counter'>(11)</span> OPTIMIZING CUTTING SPEED. The corresponding tool life for maximum production rate � ��� =. �. [(. 1 −1 �� �. �. ). �. ]. � � =�. 1 � ��� = −1 � � �. ( ).

<span class='text_page_counter'>(12)</span> OPTIMIZING CUTTING SPEED. Time elements in a machining cycle plotted as a function of cutting speed. Total cycle time per piece is minimized at a certain value of cutting speed. This is the speed for maximum production rate.

<span class='text_page_counter'>(13)</span> OPTIMIZING CUTTING SPEED Cost of part handling time. Minimizing Cost per Unit. Cost of machi ning time. Cost of tool change time. Tooling cost.

<span class='text_page_counter'>(14)</span> OPTIMIZING CUTTING SPEED Cost of part handling time. This is the cost of the time the operator spends loading and unloading the part. • The cost rate (e.g., $/min) for the operator and machine. • Part handling time • Thus the cost of part handling time:.

<span class='text_page_counter'>(15)</span> OPTIMIZING CUTTING SPEED Cost of machi ning time. This is the cost of the time the tool is engaged in machining. • The cost rate (e.g., $/min) for the operator and machine. • Machining time • Thus the cost of the cutting time cost :.

<span class='text_page_counter'>(16)</span> Cost of machi ning time. The cost of tool change time. • The cost rate (e.g., $/min) for the operator and machine. • Tool change time • : The number of pieces cut in one tool life • Thus the cost of the cutting time cost :.

<span class='text_page_counter'>(17)</span> In addition to the tool change time, the Tooling cost tool itself has a cost that must be added to the total operation cost • Tool cost per workpiece is given : the cost per cutting edge the number of pieces machined with that cutting edge. • Tooling cost requires an explanation, because it is affected by different tooling situations.

<span class='text_page_counter'>(18)</span> OPTIMIZING CUTTING SPEED For disposable inserts (e.g., cemented carbide inserts), tool cost is determined:. Tooling cost requires an explanation, because it is affected by different tooling situations. price of the insert number of cutting edges per insert. For regrindable tooling (e.g., high-speed steel solid shank tools, brazed carbidetools), the tool cost includes purchase price plus cost to regrind: : cost per tool life, $/tool life. purchase price of the solid shank tool or brazed insert, $/tool. : number of tool lives per tool. : time to grind or regrind the tool, min/tool life. grinder’s rate, $/min..

<span class='text_page_counter'>(19)</span> OPTIMIZING CUTTING SPEED The sum of the four cost components gives the total cost per unit product for the machining cycle. Cc. (*). �� =. ��. 1 �. � �� �. 1 � −1. 1 �− 1 (*). � �� � �= ��. � �� � ) ¿ ( �0 � � + �� ) ¿ � 0 � �� ��= �0 � h + ++¿ ��.

<span class='text_page_counter'>(20)</span> The cutting speed that obtains minimum cost per piece for the operation can be determined by taking the derivative of Eq. (24.12) with respect to v, setting it to zero, and solving for. � �� =0 ��. Solving. �0 � � ��� =� . 1−� � 0 � � +� �. (. The corresponding tool life is given by. ). �. ).

<span class='text_page_counter'>(21)</span> OPTIMIZING CUTTING SPEED. Cost components in a machining operation plotted as a function of cutting speed. Total cost per piece is minimized at a certain value of cutting speed. This is the speed for minimum cost per piece..

<span class='text_page_counter'>(22)</span> OPTIMIZING CUTTING SPEED. Some Comments on Machining Economics. • First, as the values of C and n increase in the Taylor tool life equation, the optimum cutting speed increases. first. • Cemented carbides and ceramic cutting tools should be used at speeds that are significantly higher than for high-speed steel tools..

<span class='text_page_counter'>(23)</span> OPTIMIZING CUTTING SPEED. Some Comments on Machining Economics. secon d. • As the tool change time and/or tooling cost ( and ) increase, the cutting speed equations yield lower values. • Lower speeds allow the tools to last longer, and it is wasteful to change tools too frequently if either the cost of tools or the time to change them is high.’’.

<span class='text_page_counter'>(24)</span> OPTIMIZING CUTTING SPEED. • (always). Some Comments on Machining Economics. Thir d. • Rather than taking the risk of cutting at a speed above or below , some machine shops strive to operate in the interval between and — an interval sometimes referred to as the ‘‘ high-efficiency range.’’.

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