Method of cold expanding and sizing fastener holes

A method of fastening a plurality of metal members together by use of a fastener having a shank and a head, comprising:

• selecting the size of fastener to be used;
• calculating a final hole sized to produce a desired fit between the final hole and the shank of the fastener;
• selecting a drill size to produce a drilled hole that is smaller than the final hole;
• using the selected drill to drill a hole in the members which are to be fastened together;
• cold expanding the drilled hole in the members by pulling a mandrel through the hole to both improve the fatigue performance of the metal surrounding the hole and to size the hole the final hole diameter after expansion is equal to the starting hole diameter plus the retained expansion;
• there being spring back shrinkage of the expanded hole to the retained expansion;
• said hole being sized by expanding the hole to at least a critical sizing expansion value which is a value of expansion beyond which the retained expansion value is linearly exceeded and to less than the same amount as the total expansion before elongation of the hole axis of the metal surrounding the hole;
• and
• installing the selected fastener in the hole.

A method of fastening a plurality of metal members together by use of a fastener having a shank and a head, comprising:

• selecting the size of the fastener;
• calculating a final hole size to produce a desired fit between the final hole and the shank of the fastener;
• selecting a drill size to produce a drilled hole smaller than the final hole which when cold expanded by use of a selected split sleeve and mandrel will become the final hole;
• using the selected drill to drill a hole through the members which are to be fastened together;
• selecting a split sleeve and a mandrel, sized such that when used to cold expand the drilled hole, will also size the hole to produce the final hole;
• inserting the selected split sleeve into the drilled hole;
• drawing the selected mandrel through the split sleeve, to expand the split sleeve and in this manner both cold expand and size the drilled hole to produce the final hole the final hole diameter after expansion is equal to the starting hole diameter plus the retained expansion;
• there being spring back shrinkage of the expanded hole to the retained expansion;
• said hole being sized by expanding the hole to at least a critical sizing expansion value which is a value of expansion beyond which the retained expansion value is linearly exceeded and to less than the same amount as the total expansion before elongation of the hole axis of the metal surrounding the hole;
• removing the split sleeve from the hole following movement of the mandrel through the split sleeve;
• and
• installing the selected fastener into the hole.

A method of cold expanding and sizing a hole in a metal workpiece to achieve the desired fit of a predetermined fastener, comprising:

• drilling a starting precision hole having a predetermined diameter;
• cold expanding the drilled hole to both improve the fatigue performance of the metal surrounding the hole and to size the hole;
• said cold expanding of the drilled hole in the workpiece is by placing a split sleeve in the hole and pulling a mandrel through the split sleeve;
• the final hole diameter after expansion being equal to the starting hole diameter plus the retained expansion, therebeing spring back shrinkage of the expanded hole to the final hole diameter;
• said hole being sized by expanding the hole to at least a critical sizing expansion value which is a value of expansion beyond which the retained expansion value is linearly exceeded and to less than the same amount as the total expansion before elongation along the hole axis of the metal surrounding the hole.

A method of fastening a plurality of metal members together by use of a fastener having a shank and a head, comprising:

• selecting the size of fastener to be used;
• calculating a final hole sized to produce a desired fit between the final hole and the shank of the fastener;
• selecting a drill size to produce a drilled hole that is smaller than the final hole;
• using the selected drill to drill a hole in the members which are to be fastened together;
• cold expanding by mandrelizing the drilled hole in the members by pulling a mandrel through the hole to both improve the fatigue performance of the metal surrounding the hole and to size the hole the final hole diameter after expansion is equal to the starting hole diameter plus the retained expansion;
• there being spring back shrinkage of the expanded hole to the retained expansion;
• said hole being sized by expanding the hole to at least a critical sizing expansion value which is a value of expansion beyond which the retained expansion value is linearly exceeded and to less than the same amount as the total expansion before elongation of the hole axis of the metal surrounding the hole;
• and
• installing the selected fastener in the hole.

A method of fastening a plurality of metal members together by use of a fastener having a shank and a head, comprising:

• selecting the size of the fastener;
• p1 calculating a final hole size to produce a desired fit between the final hole and the shank of the fastener;
• selecting a drill size to produce a drilled hole smaller than the final hole which when cold expanded by use of a selected split sleeve and mandrel will become the final hole;
• using the selected drill to drill a hole through the members which are to be fastened together;
• selecting a mandrel, sized such that when used to cold expand the drilled hole, will also size the hole to produce the final hole;
• lubricate the drilled hole and mandrel;
• drawing the selected mandrel through the drilled hole, and in this manner both cold expand and size the drilled hole to produce the final hole the final hole diameter after expansion is equal to the starting hole diameter plus the retained expansion;
• there being spring back shrinkage of the expanded hole to the retained expansion;
• said hole being sized by expanding the hole to at least a critical sizing expansion value which is a value of expansion beyond which the retained expansion value is linearly exceeded and to less than the same amount as the total expansion before elongation of the hole axis of the metal surrounding the hole;
• and
• installing the selected fastener into the hole.

A method of cold expanding and sizing a hole in a metal workpiece to achieve the desired fit of a predetermined fastener, comprising:

• drilling a starting precision hole having a predetermined diameter;
• cold expanding the drilled hole by pulling a mandrel through the hole to both improve the fatigue performance of the metal surrounding the hole and to size the hole;
• the final hole diameter after expansion being equal to the starting hole diameter plus the retained expansion, there being spring back shrinkage of the expanded hole to the final hole diameter;
• said hole being sized by expanding the hole to at least a critical sizing expansion value which is a value of expansion beyond which the retained expansion value is linearly exceeded and to less than the same amount as the total expansion before elongation along the hole axis of the metal surrounding the hole.