CPTXYGraphから継承するクラスがあり、カスタムlabl=elsを追加するために以下のメソッドを実行しました
-(void)setarLabelsEixoX:(NSArray *)labels naPosicao:(NSArray *)posicaoLabels;{
CPTXYAxisSet *axisSet = (CPTXYAxisSet *)self.axisSet;
CPTXYAxis *x = axisSet.xAxis;
x.labelingPolicy = CPTAxisLabelingPolicyNone;
NSUInteger labelLocation = 0;
NSMutableArray *customLabels = [NSMutableArray arrayWithCapacity:[labels count]];
for ( NSNumber *tickLocation in posicaoLabels ) {
CPTAxisLabel *newLabel = [[CPTAxisLabel alloc] initWithText:[labels objectAtIndex:labelLocation++] textStyle:x.labelTextStyle];
newLabel.tickLocation = [tickLocation decimalValue];
newLabel.offset = x.labelOffset;
newLabel.alignment = CPTAlignmentCenter;
[customLabels addObject:newLabel];
}
axisSet.xAxis.majorTickLocations = (NSSet*)posicaoLabels;
x.axisLabels = [NSSet setWithArray:customLabels];
}